矩镰荚苜蓿越冬期地下芽的组织化学特征与分化规律

Histochemical characteristics and differentiation of the belowground buds of Medicago archiducis-nicolai during overwintering

为了揭示矩镰荚苜蓿(Medicago archiducis-nicolai)地下芽越冬机理,采用石蜡切片法,通过组织化学染色,跟踪观测了该植物在自然越冬过程中地下芽的组织化学特征与分化过程。结果显示:在越冬期,地下芽内淀粉粒主要贮存在芽体皮层、髓部、芽尖外围幼叶、芽尖基层组织和叶原基底部,蛋白质主要贮存在芽尖生长锥、叶原基顶部和芽体形成层;秋末冷适应期,地下芽芽体快速伸长,芽内淀粉粒开始急速降解,但与其他时期相比,淀粉总含量仍处较高水平;进入初冬期后,随气温的下降,芽分化与伸长生长开始减慢,到隆冬冻胁迫期,芽锥和芽体生长停止,芽内淀粉几乎全部降解;之后随气温回升,芽体开始恢复生长,但芽锥分生生长直至返青期才开始恢复。分析表明,矩镰荚苜蓿越冬期间地下芽生长停滞和芽内淀粉粒含量降低是其休眠态转变的重要标志,休眠芽通过淀粉粒水解代谢,增加细胞可溶性糖浓度、降低细胞冰点是其抵御冬季低温胁迫的适应机制。

To determine the mechanisms underlying belowground bud overwintering in Medicago archiducis-nicolai,we examined the histochemical characteristics and differentiation of buds during the period of overwintering,based on the histochemical staining of paraffin sections.Observations revealed that the starch content in overwintering buds is stored primarily in the cortex,pith,the peripheral young leaves and basal tissue of bud tips,and in the basal part of the leaf primordium,whereas protein is mainly stored in the growth cone of bud tips,apical leaf primordia,and cambium of the bud body.At the cold-adaptation stage in late autumn,the bud body was observed to undergo rapid elongation and starch in the buds began to undergo degradation,although total starch contents remained at a high level during this stage.At the beginning of winter,there was a retardation in both bud differentiation and elongation,concomitant with a reduction in temperatures.At the freezing-stress stage in winter,there was a cessation of growth in both the bud cone and bud body,and at this stage,the starch content of buds had been almost completely degraded.Thereafter,in response to gradually increasing temperatures,the bud body slowly began to resume growth,although meristematic growth of the bud cone did not recover fully until the growing stage in spring.In conclusion,our findings indicated that in belowground buds of M.archiducis-nicolai,the transition to a dormant state is characterized by growth stagnation and a reduction in the starch contents of buds,and that dormant buds can withstand cold stress during the period of overwintering on the Qinghai-Tibet Plateau.This cold tolerance can be attributed to the degradation of starch in buds,which,by increasing the concentration of soluble sugars in cells,contributes to reducing their freezing point.