Plants are incapable to maintain their cell and tissues at a constant optimum temperature like human and animal , their metabolism , growth and development are affected by change in environmental (Fitter and Hay , 2002).The distribution of complex in environmental and plant temperatures, it is difficult to determine the temperature relation of plant processes in the field over periods of days or weeks. Plant growth and reproduction can depend on one or more of range of thermal parameters, including : mean, minimum and maximum temperature, and amount of accumulated temperature (thermal time ; degree days ) above a threshold during the whole growing season, or a shorter critical phase such as seed production (Fitter and Hay , 2002).
The component processes of plant growth do not all respond to temperature in the same way . For instance , in most temperate crop species, gross photosynthesis stopped at temperature just below 0 â-¦C (minimum) and above 40 â-¦C (maximum), with the highest rates being achieved in the range 20-35 â-¦C. On the other hand , rates of respiration tend to be low below 20 â-¦C but , owing to the thermal disruption of metabolic controls and compartmentation at higher temperation, they rise sharply up to the compensation temperature at which the rate of respiration equals the rate of gross photosynthesis, and there can be no net photosynthesis (Fitter and Hay , 2002).
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The complexity of the thermal environment of plants is linked by the complexity of their response to temperature. (Fitter and Hay , 2002).
1-How plants sense temperature
Plants are effect to physical change in their environment. In seasons the temperatures are vary from period to another period and in general over any 24-h period low night temperatures alternate with higher daylight temperatures (Ruelland and Zachowski , 2010).
The change of temperature have a biggest effect on cell physiology (Ruelland and Zachowski , 2010). Heat causes denature of proteins ,also effect metabolism, membrane fluidity, and cytoskeleton rearrangement. The damaging impacts, on both vegetative and reproductive tissues because change consequence of cold and heat (Ruelland et al., 2009; Wahid et al., 2007; Zinn et al., 2010). The change of temperature play important role in reset of internal clocks (Thines and Harmon, 2010).
The plants can survive exposure to temperatures above those optimal for growth or acquire tolerance to otherwise lethal heat stress (Larkindale et al., 2005). Plants can survive exposure to temperatures above optimal temperature is linked with accumulation of solutes and increases in the antioxidant capacity (Wahid et al., 2007; Kotak et al., 2007; Guy et al., 2008; Allakhverdiev et al., 2008; Rampino et al., 2009; Frank et al., 2009).
- Changes in membrane fluidity trigger temperature responses
The moving mosaics of proteins and lipids are called Membranes . Lipids flip-flop between monolayers, spread within the plane of a monolayer, and rotate about their own axes, with their acyl chains also rotating around C-C bonds. Each kind of motion is thermodynamically driven with its own temperature dependence, i.e. its activation energy (Ruelland and Zachowski , 2010). When the temperature high , lipid movement will be faster and membranes will be more fluid (Vigh et al., 2007).
It is very interesting, membrane fluidization is way of sensing heat. So the heat sensing signed through protein unfolding. The heat activation of a Heat-activated MAP kinase (HAMK) is mediator of heat shock response to induces Ca2+ . The heat activation of a Heat-activated MAP kinase (HAMK) and the heat-stress protein HSP70 were featured to be antagonized by dimethylsulfoxide (DMSO), while they are simulated at control temperature by benzyl alcohol (BA) (Sangwan et al., 2002; Suri and Dhindsa, 2008). In Physcomitrella patens, benzyl alcohol (BA) induces Ca2+ entry .So will be response to heat and heat tolerance (Saidi et al., 2009). Therefore, membrane fluidity is a sensing device of heat (Ruelland and Zachowski , 2010).
1.2 - Protein conformation changes with temperature
Protein unfolding will be result from up shift and downshift of temperature (Pastore et al., 2007). During it the protein denaturation acts as a trigger for many responses to heat. It is very interesting, it is possible to Create misfolded proteins through the use of the proline analog l-azetidine-2-carboxylic acid (AZC). It was possible , significant overlap between heat stress-responsive genes and AZC-responsive genes by a transcriptomic analysis, shows the protein unfolding pathway is a subcomponent of the heat stress response (Sugio et al., 2009).The AZC-responsive genes is heat shock factor , also it is transcription factor. Proposed that heat-induced protein denaturation could involved to the activation of some heat stress transcription factors (HSTF). When the temperature is rise can be directly sensed by proteins acting as effectors of the heat response (Lee et al., 2009; Park et al., 2009). Final the heat-induced protein denaturation as heat perception step (Ruelland and Zachowski , 2010).
1.3 - Temperature changes induce disassembly of the cytoskeleton
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The temperature will be affecting in activity of protein, Also the temperature will also impact peptide structures(Ruelland and Zachowski , 2010). It is very interesting, heat has a resemble effect on the cytoskeleton: when temperature move from 27 â-¦C to 42â-¦C resulted in the disruption of the majority of microtubules in tobacco cells after 30 min, Also , as in Arabidopsis roots moved from 20 â-¦C to 42â-¦C (Smertenko et al., 1997; Müller et al., 2007).
Are these cytoskeleton disequilibria caused by temperature changes upstream of the response to heat? In the heat response, heat activated MAP-kinase; (HAMK) activation at 37 â-¦C is prevented by taxol, Whereas destabilizing microfilaments or microtubules activates heat activated MAP-kinase; (HAMK) at 25 â-¦C (Sangwan et al., 2002). The heat-response accumulation of heat stress protein 70 (HSP70) and heat-activation of heat activated MAP-kinase (HAMK) need disassembly of the cytoskeleton (Suri and Dhindsa, 2008).
1.4 - Effects of temperature change on metabolic reactions including photosynthesis
Cell metabolism is control by the activity of enzymes. The activity of enzymes are temperature dependent. This is due to both unfolding/ inactivation of enzymes and to change in catalytic rate .This temperature dependency can be features by the Q10-value, i.e. the factor by which enzyme activity is increased when temperature is rise by 10 â-¦C. Q10 values may be very different among enzymes (Ruelland and Zachowski , 2010). So, cell metabolism is affected by temperature effects on enzyme activities. These change may generate signalling pathways triggering heat responses (Ruelland and Zachowski , 2010).
Through photosynthesis, CO2 together with ribulose-1,5- bisphosphate to produce glycerate-3-phosphate, which is reduced into triose-phosphates. Most of the triose-phosphates are maintainedin the chloroplast, with the remainder mainly being exported to the cytosol and transferred into sucrose. This conversion releases inorganic phosphate (Pi) that returns to the chloroplast for ATP synthesis. The regeneration of Pi is important for optimal carbon Fixation (Ruelland and Zachowski , 2010).
In the heat, it prevent photosynthesis (Sage and Kubien, 2007; Yamori et al., 2009; Yamori et al., 2010; Zhang and Sharkey, 2009; Salvucci, 2008). This lead to a lower in Rubisco activation (Salvucci and Crafts-Brandner, 2004; Salvucci et al., 2006; Yamori et al., 2009) as increase temperatures prevent Rubisco activase (Salvucci and Crafts-Brandner, 2004; Salvucci et al., 2006; Kurek et al., 2007; Kumar et al., 2009). This latter enzyme is indeed exceptionally sensitive to thermal denaturation, even at moderate temperatures (Salvucci et al., 2001).
Fig. 1. (Ruelland and Zachowski , 2010).
In Figure 1 , schematic representation of the temperature sensing machinery in plants. heat sensing mechanisms in plants are the very same cellular processes disturbed by a temperature change. We have identified membrane fluidity, protein conformation, cytoskeleton affected by heat and upstream of cellular responses to these temperature changes. The signalling pathways downstream of the sensing steps can also influence these sensing steps. The cellular responses activated in response to heat will participate in switching off the temperature sensing devices (Ruelland and Zachowski , 2010).
2-Effects of lighting and air movement on temperatures in reproductive organs of plants in a closed plant growth facility
Plant growth and reproduction in space have been of high concern as the possibility rise for long-term manned space flights. The feasibility of maintaining long-term manned space missions is dependent on growing crops in space farms that will provide food or Bioregenerative Life Support Systems (BLSS), CO2/O2 transfer and water purification (Kitaya and Hirai ,2007). For space farming, the transition of gases and heat between their environment and plant surfaces is impact by the absence of buoyancy dependent convective transport, limited ventilation and increase ethylene concentrations in plant growth facilities making poor yields in space and poor development of plant reproductive organs (Monje et al., 2003).
On the earth, convection happen with unequal distribution of temperature. Air movements are caused by the convection even in a closed chamber with no forced ventilation system. There is, nevertheless, no natural convective or thermal mixing under microgravity conditions in space because buoyancy is regarded to be negligible under microgravity conditions. The limited convection would decrease plant growth by limiting gas exchange and heat on plant leaves. Effective air movement in a closed plant production system is so important to enhance the gas exchange and heat between ambient air and the plants, and consequently promote growth of plants in space(Kitaya and Hirai ,2007).
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The impact of air movement and illumination on the temperature high in petals, anthers and stigmas of plant reproductive organs were achieved under normal gravity conditions (Kitaya and Hirai ,2007).
In experiment of impact of lighting on the temperature of reproductive organs of strawberry on the high temperature. The result will be temperatures of stigmas and anthers were lower than that of petals of strawberry plant. The reason of that , petals facing the light source presented the highest temperatures .The temperature began to increase just after lamp turned on (after 4 min).Therefore the temperature increase more faster in petals than anther and stigmas (Kitaya and Hirai ,2007).
The another experiment of impact of air movement on the temperature of reproductive organs and leaves of both strawberry and rice. The result will be temperatures of reproductive organs and leaves of strawberry were significantly higher than those of rice. Temperatures of reproductive organs and leaves reduce with more air velocities. For strawberry, the temperatures of petals, stigmas, anthers and leaves decreased by when the air velocity increased from 0.1 to 1.0 ms-1. For rice, the temperatures of glumes, stigmas, anthers and leaves decreased when the air velocity increased from 0.1 to 1.0 ms-1 (Kitaya and Hirai ,2007).
The experiment confirmed the importance of air movement for decrease temperatures of reproductive organs (Kitaya and Hirai ,2007). The noted temperature increases would be larger for smaller organs such as stigmas and anthers under microgravity conditions. Leaf temperature increase under microgravity condition was more significant at the narrower region of the leaf blade of barley due to the higher resistances to heat transfer and water vapor in the leaf boundary layer (Kitaya et al., 2006).
In the present study, it was confirmed that air movement was important to avoid temperature increases in leaves and plant reproductive organs. Also decrease air convection under microgravity conditions in space would limit plant growth by decrease heat and gas exchanges between plant organs and the ambient air. Proper air movement is important to promote plant growth during vegetative and reproductive growth stages (Kitaya and Hirai ,2007).
3- C3 and C4 photosynthesis of temperature response
Best controls of over plant distribution and productivity is temperature(Sage and Kubien ,2007). In general, In plants from hot environments, for example summer and tropical species, photosynthesis work between 15 and 45 Â°C with no obvious problem (Berry and Raison 1981;Downton,Berry and Seemann 1984; Bunce 2000).
But other species, like as species for special environments, show less potential to acclimate (Atkin et al. 2006). Finally, at temperatures beside the extreme end of the functional group, injury happen, and photosynthesis rate is not reverse (Sage and Kubien ,2007).
3.1 - Theortical controls on photosynthetic capacity in C3 plants
In the leaves of C3 , the rate of net CO2 assimilation (A) therefore the plants is normally characterized under the control of three essential steps: first step is the capacity of ribulose 1.5- bisphosphate oxygenase / carboxylase (Rubisco) to consuming ribulose bisphosphate (RuBP) (RuBP-saturated photosynthesis or Rubisco-limited photosynthesis). Meaning of RuBP is molecule that carban dioxide react with photosynthesis carbon fixation. The second step is the Capabilities of the Calvin cycle and last step is the capacity of sucrose and starch composition to consuming renewal inorganic phosphate Pi and triose phosphates for photophosphorylation is production of ATP (Harley & Sharkey 1991; von Caemmerer 2000).
Distinctive responses of A to CO2 and O2 variation in leaves of C3 suggests whether A is limited by the regeneration capacity of RuBP and Pi regeneration capacity. When A is oversighted by RuBP regeneration capacity, it is motivate by a reduction in O2 or an high in CO2 supply below conditions where photorespiration happens (von Caemmerer & Farquhar 1981; Sharkey 1988). The RuBP renovation-limited A to O2 and CO2 reflecting the competition between these gases for RuBP; as levels of CO2 will be very high, The enzyme called oxygenase activity is increasing not stimulate and A will increase with the slope of decreasing to a plateau that become at the CO2 level where photorespiration being nil. On the contrary, when A is restricted by the capacity of Pi regeneration, there is few if any motivate following CO2 fertilization or O2 minimize at CO2 levels when photorespiration is starting (Sharkey 1985a,b, 1988).This shortage of CO2 or O2 sensitivity happen due to Pi is used as fast as it being present , a situation that is not changed by decrease photorespiration (Sharkey 1985b).
3.2 - Adaptation of C3 photosynthesis to modified in growth temperature:-
Many plant species are capable to adapt to change in growth temperature by changing the photosynthetic system. In normal, following a change in growth conditions by 5-10 Â°C, the thermal optimum moved in the way of the new temperature of growth , and the average of A be increase at the growth temperature however the rate of the thermal optimum will decreases (Regehr and Bazzaz 1976; Berry and Björkman 1980; Mawson et al. 1986; Yamori et al. 2005). Differences are obvious depending on species and growth conditions.
An essential component of thermal adaptation is an changing in membrane composition to move the thermal domain where membranes will be fluid yet constant towards the growth temperature. Between 20 and 40 Â°C, this is achievement by changing the rate of saturated to be unsaturated fatty acids in the lipid matrix (Huner 1988; Mikami and Murata 2003). Saturation of fatty acids will be increases the hydrophobic interactions between adjacent fatty acids, and will increasing the rigidity of the membrane (Hochachka and Somero 2002). Therefore this cause, increasing saturation of fatty acids is looked an acclimation response to increase temperatures and is connect with higher thermotolerance in a large domain of species (Sharkey and Schrader 2006). When saturation of fatty acids will increase , At lower temperatures will be damage the fluidity , while with a potential for decreased constant and rotation of membrane-bound enzymes (Mitchell and Barber 1986).
Adaptation connected with change in fatty acid Formation is comparatively slow, needing to hours or a few days to be active. As like, this mechanism of adaptation is very slow to responds to fast change in temperature of leaf at different period of day, as may happen in response to sudden buildup in light level or a low speed wind ( Wise et al. 2004; Sharkey 2005). The average of respiration in the light also adaption to increasing temperature. The rate of Respiration normally rise with measurement temperature; however, day respiration lower in many species following growth at high temperature, and may approach the rate showed at the original growth temperature (Atkin et al. 2005, 2006). This change impacts the thermal response of A, especially in plants leaves thick and decrease of photosynthetic capacities, like as conifers (Way and Sage, unpublished data).
3.3 - Temperature response of C4 photosynthesis
In C4 plants, photosynthetic carbon absorption reflects the Rubisco activty in vivo(inside the tissue) , as it does in C3 plants. Nevertheless, because Rubisco is closed in a sealed compartment where CO2 is fixed to near- saturation levels, the photosynthetic restriction vary . At low CO2, A is expected to be unlimited by the phosphoenolpyruvate capacity (PEP) carboxylase (PEPCase) to fix bicarbonate for motion into the sheath of bundle as part of a C4 acid (von Caemmerer 2000). The activity of PEPCase is independent of temperature at decrease level of CO2 (Laisk and Edwards 1997). And thus, the CO2 response primary slope of A in C4 plants is bigger sensitivity to temperature (Long and Woolhouse 1978;Sage 2002)
Oxygenase activity is significantly suppressed in C4 plants, and as a consequence, the CO2 compensation point does not increase noticeably with temperature as it in C3 plants. At in CO2 compensation point the uptake of CO2 through photosynthesis pathways is exactly matched to respiratory release of CO2 and uptake of O2 by respiration is exactly matched to photosynthesis release of oxygen. This, in link with the thermally sensitivity response of the primary slope, reasons the temperature response of A at lower CO2 to be comparatively flat in C4 plants (Sage 2002). This generally happen at lower atmospheric CO2 levels corresponding to late-Pleistocene (180 mbar) and pre-Industrial (270 mbar) time. To high temperature sensitivity, the photosynthesis average of C4 plants has to be upper the CO2 saturation point (Sage 2002). Rubisco act as carboxylation (carboxylic acid introduce in substrate) or oxygenation (increase O2 tissue ).Rubisco is very important to biological impact because it catalyze chemical reaction and inorganic carbon .This two factor important role in biosphere.
1-Some advances in plant stress physiology and their implications in the systems biology era
The molecular biology is to make its provide serve for humankind benefits timely and efficiently (Boudsocq et.al ,2005 , Bo Shao et.al , 2007). Plant stress physiology is increasing its importance and gaining its attention on the globe under global climate change ( Bo Shao et.al , 2006).
4.1 - Osmotic signaling mediated by second messengers and kinases families in plants
the most important abiotic stresses for crop yields worries about plant dehydration (Boudsocq et.al ,2005 , Bo Shao et.al , 2007). Plants suffering from dehydration under the condition of high salinity, drought, and low-temperatures, all of which cause hyper-osmotic stress features by a decreased turgor pressure and water loss ( Huq , 2005 , Bo Shao et.al , 2007). Dehydration triggers the biosynthesis of the abiscisic acid ABA hormone and it has been known for a long time that a set of genes, caused by the drought, salt, and cold stresses, are also activated by abiscisic acid (ABA) (Boudsocq et.al ,2005 , Bo Shao et.al , 2007). The application of common components and pathways in plant responses to Linked stresses allows plants (crops) to acclimate partly to a wide range of harmful conditions after exposure to only one specific stress (Boudsocq et.al ,2005 , Bo Shao et.al , 2007).Furthermore, to these common signaling elements, highly specific signaling mechanisms occur and newly recognized linked genes can also act in the process, allowing exact plant adaptation (Gregory, 2006 , Bo Shao et.al , 2007). For example , many genes caused by the by salt, drought, UV-B radiation, and cold stress are not responsive to exogenous ABA treatment, indicating the existence of ABA-independent signal transduction cascades besides the ABA-mediated pathways (Boudsocq et.al ,2005 , Bo Shao et.al , 2007).
Signal perception at the plasma membrane result to the production of second messengers that initiate cascades of signaling events(Chen et.al, 2004 , Bo Shao et.al , 2007). It was shown that osmotic stresses caused by the calcium fluxes(Boudsocq et.al ,2005 , Bo Shao et.al , 2007). The calcium signal results from extracellular calcium influx and/or calcium release from intracellular pools (Carafoli, 2004 , Bo Shao et.al , 2007). IP3 is activation vacuolar calcium channels and it was proposed that calcium is released from intracellular pools in response to hyperosmotic stresses the result of the activation of the IP3 dependent calcium channels (Boudsocq et.al ,2005 , Bo Shao et.al , 2007).
Other phospholipids, especially phosphatidic acid (PA), Appear to have significant roles in osmotic signaling (Boudsocq et.al ,2005 , Bo Shao et.al , 2007). phosphatidic acid (PA) was reported to accumulate in response to cold treatment and water deficit . It can be formed directly by phospholipase D or indirectly by phospholipase C after phosphorylation of diacylglycerol (Boudsocq et.al ,2005 , Bo Shao et.al , 2007). A modern study using PA affinity chromatography identified Many transduction proteins like kinases, phophatases, and 14-3-3 proteins as potential PA targets (Boudsocq et.al ,2005 , Bo Shao et.al , 2007).
In conclusion, I discuss Plant physiological responses to high temperature stress. Firstly, I talked about how plants sense temperature. Confronted to changes in temperatures, plants readjust their biochemical makeup to adapt and survive. plant cells have an integrated network of temperature-sensing devices that trigger short-term responses and long-term acclimation for living with ever-changing temperatures. These devices are the very cellular features that are change by temperature change. The switching-on of these devices create a temporal and spatial network of responses to temperature change, resulting to adapted responses that will result to a new cellular equilibrium. However, the way those devices, once switched on, can activate signalling pathways are still to be discovered.
Secondly, I discuss effects of lighting and air movement on temperatures in reproductive organs of plants in a closed plant growth facility. They reached to
Increases of temperature in plant reproductive organs like anthers and stigmas should cause fertility impediments and so produce sterile seeds under artificial lighting conditions without sufficient controlled environments in closed plant growth facilities. There are a possibility like a situation could happen in Bioregenerative Life Support Systems below microgravity conditions in space because there will be slightly thermal mixing or natural convective. This study was conducted to select the temperature of the plant reproductive organs as impacted by lighting and air movement under normal gravitational forces on the earth and to create an estimation of the temperature increase in reproductive organs in closed plant growth facilities under microgravity in space. The temperatures of petals, stigmas, anthers and leaves of strawberry . Temperatures of reproductive leaves and organs of strawberry were significantly higher than those of rice. These results show that air movement is important to decrase the temperatures of plant reproductive organs in plant growth facilities.
Thirdly, I discuss about the temperature response of C3 and C4 photosynthesis. Lead to photosynthesis across thermal domain that do not damage the apparatus of photosynthetic.
In C3 species, photosynthesis is classically examined to be ability of limited by capacity of ribulose 1.5-bisphosphate oxygenase / carboxylase (Rubisco), ribulose bisphosphate (RuBP) regeneration or Pi regeneration.Upper of the thermal optimum, adaption of A to increase growth temperature is linked when heat stability of Rubisco activase and/or electron transport capacity will be increased.
Controlling the temperature response of photosynthesis of land plants. Whereas there is a best commonly knowledge of the potential limitations, main area especially with respect to limitations at temperatures above the optimum. In near future, efforts should be made to clarify the limitations on A upper of the thermal optimum, especially, the importance of electron transport versus ability of Rubisco activase.
finally, I discuss about some advances in plant stress physiology and their implications in the systems biology era. Plant physiology cannot be replacement by modern molecular biology, on the contrary it must be enhanced in the systems biology era for developing the world eco-environment and feeding the increasing world population under climate modifed. Farmers have long known that often it is the simultaneous occurrence of many abiotic and/or biotic stresses, instead of a special stress condition, that is lethal to crops. Until now, the co-occurrence of various stresses is rarely addressed by biotechnologists and molecular biologists that study adaptation of plant.