NaCl在四翅滨藜适应渗透胁迫中的作用

泌盐盐生植物四翅滨藜是一种多年生C₄灌木,具有良好的适应盐碱和干旱环境的能力。前期研究发现,通过将过量Na⁺转运至叶表面盐囊泡、增加Na⁺对渗透势的贡献以提高植株保水能力是四翅滨藜耐盐的主要策略,且100 mmol·L^-1 NaCl可显著刺激其生长。为进一步探究NaCl是否有助于缓解渗透胁迫对四翅滨藜生长的不利影响,本研究分别用不含和含有100 mmol·L^-1 NaCl的山梨醇引起的总渗透势为-0.2和-0.5 MPa的1/2 Hoagland营养液处理5周龄四翅滨藜幼苗5 d。结果表明,在渗透胁迫下,NaCl的添加可增加叶片相对含水量、提高净光合速率以及降低叶渗透势(Ψ_s),从而促进四翅滨藜的生长。NaCl的添加还显著增加了茎叶组织及叶盐囊泡中的Na⁺积累并提高了Na⁺对叶Ψ_s的贡献,且对茎叶组织中K⁺含量影响较小。此外,渗透胁迫下,添加一定浓度NaCl显著增加了植株中游离脯氨酸和甜菜碱含量,它们除作为保护剂减轻渗透胁迫损伤外,还参与植株的渗透调节,从而进一步提高四翅滨藜对渗透胁迫的适应性。综上所述,适宜浓度的NaCl的确能够有效缓解渗透胁迫对四翅滨藜生长的不利影响。

Effect of NaCl on the adaption of Atriplex canescens under osmotic stress

Secretohalophyte Atriplex canescens is a C₄ perennial shrub with excellent resistance to salinity and drought. Our previous study showed that the transport of excessive Na⁺ into leaf salt bladders and contribution of the elevated Na⁺ concentration to leaf osmotic potential (Ψ_s) improves water status of plants and is a primary strategy in salt tolerance of A. canescens. The external application of 100 mmol·L^-1 NaCl can substantially stimulate the growth of A. canescens. To investigate whether NaCl could help to alleviate deleterious impacts of osmotic stress on the growth of A. canescens, five-week-old seedlings were subjected to two osmotic stress levels (-0.2 and -0.5 MPa) induced by D-sorbitol in the presence or absence of an additional 100 mmol·L^-1 NaCl. It was found that under osmotic stress, the addition of NaCl obviously improved the growth of A. canescens. Leaf relative water content was increased, net photosynthetic rate was enhanced and significantly more negative Ψ_s was induced. Furthermore, exogenous NaCl significantly increased Na⁺ concentration in stem, leaf tissues and leaf salt bladders as well as enhancing the Na⁺ contribution to leaf Ψ_s, with little adverse effect on K⁺ accumulation in stem and leaf tissues. In addition, the content of free proline and betaine in plants was significantly increased in the presence of NaCl under osmotic stress, and their contributions to leaf Ψ_s were significantly increased by additional NaCl under osmotic stress. This suggests that compatible solutes, in addition to functioning as protectants, are also involved in osmotic adjustment to further alleviate the deleterious impacts of osmotic stress. In summary, the appropriate concentration of NaCl does effectively alleviate the adverse impacts of osmotic stress on the growth of A. canescens.