| Some halophytes such as some euhalophytes are markedly succulent undersalinity condition. Succulent euhalophyte can not only dilute salt solution to decreasesalinity toxicity but also store water to maintain normal physiological processes.Similarly, many plants, especially CAM plants, also are succulent to maintain normalphysiological processes under drought environments. CAM plants can survive in aridand semi-arid zone, whose stems and leaves are frequently high succulent and store alot of water, as a result, CAM plants can exist in extra drought press condition. Itindicates that succulence plays an important role in various aspects of plant growthand metabolism under stress environments. There are many viewpoints on the reasonsof succulence, but there is no uniformal conclusion on it. In the present study,glycophyte K. daigremontiana grown under different NaCl treatments, natrualdrought and iso-osmotic NaCl treatments was used to investigate K. daigremontianagrowth, water, ion, organic acid content, soluble sugar content, succulence,photosynthesis and chlorophyll fluorescence. The aim was to determine the effect ofNaCl treatments on K. daigremontiana and the mechanism of succulence. The mainresults are shown as follows:1. Effect of natural drought and NaCl treatments on the leaf succulence ofK. daigremontianaUnder natural drought treatment, the leaf parenchyma was obviously bigger thancontrol, and the eaf water content was also significantly increased. Leaf succulentdegree was significantly enhanced compared with the control. On the other hand, theleaf parenchyma has no distinct changes compared with the control under iso-osmoticNaCl treatments. The leaves of K. daigremontiana were not obviously succulent.There were strong effects on the succulent degree of K. daigremontiana treated with200 mmol/L NaCl, the seedlings and leaves were smaller than the control. The leafsucculent degree was also markedly decreased. It indicates that natural drought stressstimulates the succulent of K. daigremontiana, while iso-osmotic NaCl treatment hasno effects on the succulent of K. daigremontiana. However, 200 mmol/L NaCltreatments lead to significant decrease of the succulent degree.2. Effect of natural drought and NaCl treatments on the leaf water contentand relative water content of K. daigremontianaThe leaf water content and relative water content were significantly increasedunder natural drought stress, but no distinct changes were observed under iso-osmoticNaCl treatment. However, under 200 mmol/L NaCl treatment, the leaf water contentand relative water content were markedly decreased compared with the control. Itindicates that natural drought stress promotes leaf water content, but iso-osmotic NaCltreatment has no obvious effects on the water content of K. daigremontiana leaves.Furthermore, high concentration NaCl treatment (200 mmol/L) markedly decreasedthe water content of K. daigremontiana.3. Effect of natural drought and NaCl treatments on leaf osmolytes of K.daigremontianaCompared with control plants, the Ca2+,K+ and organic acid content of K.daigremontiana were significantly increased under natural drought treatment. Innonhalophytes, K+ may work as osmolyte to regulate the osmotic potential ofcytoplast and vacuole. Natural drought treatment promotes K. daigremontianaaccumulating Ca2+,K+ content and producing organic acid. Under iso-osmotic NaClenvironment, no clear changes in organic acid content was detected;the succulentdegree of K. daigremontiana was also not distinctly affected. The K+ content andorganic acid content were evidently decreased with 200mmol/L NaCl treatments.200mmol/L NaCl significantly decreased K+ uptake and organic osomolyte contentsuch organic acid, thus the succulent degree of K. daigremontiana markedly wasdecreased.4. Effect of natural drought and NaCl treatments on the leaf osmoticpotential of cell sap of K. daigremontianaIn natural drought environment, the osmotic potential of the leaf cell sap of K.daigremontiana strongly was decreased, while the osmotic potential of the leaf cellsap of K. daigremontiana was not significantly changed under iso-osmotic NaClenvironments. 200 mmol/L NaCl treatment led to drastically decrease of the osmoticpotential of the leaf cell sap of K. daigremontiana. However, it was still higher thanthe osmotic potential of soil. It suggests that K. daigremontiana could not produceenough osmolytes to adjust the cell water potential for water uptake under high NaCltreatment.5. Effects of natural drought and NaCl treatments on the photosyntheticparameters of K. daigremontianaUnder natural droughtcondition, the stomatal conductance (GS) and Netphotosynthetic rate of K. daigremontiana were strongly increased, but neither wassignificantly affected by iso-osmotic NaCl treatments. 200 mmol/L NaCl stresssignificantly increased Fo compared with the control in light but not recovered to thelevel of control at night. Fv/Fm was also drastically decreased by 200 mmol/L NaClstress. The results showed that 200mmol/L NaCl stress damaged photosyntheticapparatus,and chlorophyll content was drastically decreased . As a result, 200mmol/LNaCl stress drastically decreased the net photosynthetic rate of K. daigremontiana.Natural drought and iso-osmotic NaCl treatments had no effects on Fo and Fv/Fm.In conclusion, natural drought treatment promoted the succulent degree of K.daigremontiana while iso-osmotic NaCl treatment had no obvious effects on thesucculent degree of K. daigremontiana;200mmol/L NaCl stress drastically decreasedthe succulent degree of K. daigremontiana. Investigations of water content, relativewater content, cell sap osmotic potential, microstructure of leaf and photosyntheticparameters indicated that natural drought treatment promoted the net photosyntheticrate of K. daigremontiana. The organic acid content of K. daigremontiana wasincreased, thus the osmotic potential of vacuole was decreased. All this wouldcontribute to leaf water uptake, so leaf water content and relative water content weresignificantly increased. Consequently, the succulent degree of K. daigremontianasignificantly increased. On the other hand, 200mmol/L NaCl stress damagedphotosynthetic apparatus of K. daigremontiana. The net photosynthetic rates, organicacid content of K. daigremontiana were markedly decreased. Theses results suggestedthat K. daigremontiana can not produce enough compatible solutes to maintain lowerosmotic potential. Leaf cell cannot uptake water;therefore the succulent degree of K.daigremontiana was significantly decreased. Iso-osmotic NaCl treatment had nosignificant effects on the net photosynthetic rate, organic acid content and osmoticpotential of K. daigremontiana, thus the succulent degree of K. daigremontiana wasnot significantly increased. As far as we know, we can confer that there is a closerelation between the organic acid content and the succulent degree, rather than ioniccontent such as Na+, which is distinctly different from the halophyte succulencesuch Suaeda salsa under salinity.
|
PDF Full Text Request