Physiological and functional root traits that are related to drought tolerance and their genetic bases in crop plants

根信号的产生一系列盆栽和田间试验表明，在水稻植株中，在部分根系暴露于干燥条件而其余根系可接触水的条件下，气孔导度的降低和叶片和木质部分泌物中阿坝浓度的增加早于叶水势的明显下降。在干燥的土壤中断根可使气孔导度和叶水势恢复。这些事实有力地表明，阿坝在干旱土壤中产生于根中，并作为根的化学信号，根系可塑性在干旱适应中的功能意义--54个染色体片段代换系（CSSL）来自Nipponbare和Kasalath由国立农业生物科学研究所创建的用于检查对干旱胁迫的发育和生理反应，并筛选出根系可塑性发育在植物适应逆境中起重要作用的品系。这些品系与日本晴回交，为进一步的遗传分析和育种准备材料。同时，还对影响侧根可塑性的几个QTL进行了定位，并对根系渗透调节作为侧根可塑性的生理基础进行了研究。还发现有非洲新稻利用CSSLs研究了水稻对土壤水分波动的适应性，筛选出了通气组织形成、向根尖输氧、在水培、土培和大田条件下，侧根发育的可塑性较强。

Root signal productionA series of pot and field experiments showed that in rice plants, the decrease in stomatal conductance and the increase in ABA concentration in leaf and xylem exudates were detected earlier than apparently drop of leaf water potential under the conditions where a part of root system was exposed to drying conditions while the rest was accessible to water. Severing the roots in the drying soil resulted in recovery of the stomatal conductance as well as leaf water potential. These facts strongly suggest that ABA was produced in the roots in the dry soil and worked as root chemical signal, and regulated stomatal opening together with hydraulic signal that was also coming from the roots.Functional significance of root plasticity in drought adaptationFifty four Chromosome Segment Substitution Lines (CSSL) derived from Nipponbare and Kasalath created by the National Institute of Agrobiological Sciences were used to examine developmental and physiological responses to drought stress, and we screened several lines that showed significant roles of plastic development of root system in plans' adaptation to the stress conditions. Those lines were backcrossed with Nipponbare to prepare materials for further genetic analysis and breeding. Further, several QTLs that are responsible for the lateral root plasticity were identified, and root osmotic adjustment as physiological basis for the plasticity was also studied. It was also found that there were NERICA (New Rice for Africa) lines in which such plastic root responses played key roles in the plants' growth under drought.Ability of oxygen transport in rootsBy using the CSSLs, we examined the rice plant adaptation to soil moisture fluctuations and screened several lines that showed adaptability through high ability in aerenchyma formation, oxygen transport to root tip, and plastic lateral root development under hydroponic, soil culture and field conditions.