松科植物对干旱胁迫的反应

水分亏缺是制约树木生长的重要环境因子，植物通过形态、生理以及分子水平来适应水分亏缺．渗透调节使植物在低水势下维持正常生理活动，是植物忍耐水分亏缺的重要生理机制．干旱胁迫下，植物形态结构变化有利于水分吸收和传导，从而提高水分利用效率；同时，生物量向根部的分配增加，叶面积/边材面积比发生变化，这种生物量分配转移提高了根和茎向叶片输水能力，从而防止气穴现象；干旱胁迫容易引起光能过剩，过剩的光能会对光合器官产生潜在的危害．依赖于叶黄素循环的热耗散是光保护的主要途径；同时酶促及非酶促系统也是防止光合器官破坏的重要途径；脱落酸作为一种激素逆境信号，活化了与抗旱诱导有关的基因．本文从形态变化、渗透调节、气穴现象、光合作用、水分利用效率、脱落酸以及分子机理等方面阐述了松科植物对干旱胁迫的响应，并对耐旱指标的筛选进行了讨论，干旱胁迫下，各耐旱机理相互制约，需要联合各个方面的因素来考虑整个植物对干旱的反应．参99。

RESPONSES OF CONIFERS TO DROUGHT STRESS

Drought stress is one of the major environmental stresses that affect plant survival and growth. The effects of drought can be mitigated by a number of strategies, including morphological, physiological and molecular acclimation to drought. Many species exhibit changes in partitioning in favor of the structures involved in water uptake and transport, and increase water use efficiency (WUE) in response to water deficits. Greater allocation to root system may increase the amount of soil water accessible for a plant. Changes in foliage area/sapwood area ratio also involve in the water potential gradient from root to shoot. Synthesis and accumulation of osmoprotectants can increase the drought tolerance of plant. Osmotic adjustment in response to drought stress allows the normal functioning of physiological processes to take place. Xanthophylls cycle-dependent thermal dissipation and the integrated system of enzymatic and non-enzymatic antioxidants are involved in the photoprotective mechanisms during the periods of drought. Water-stress related genes are induced by abscisic acid (ABA), which apparently is involved in the signal transduction during drought stress. In this review, we examine the roles of morphological changes, osmotic adjustment, xylem cavitation, photosynthesis, WUE, ABA and molecular mechanism for acclimation and adaptation of conifers to drought stress. Moreover, the use of physiological characteristics as selection criteria for drought tolerance is also discussed. During water stress, drought-tolerant mechanisms are not independent and they are needed to integrate different aspects about whole plant responses. Ref 99