| dc.description.abstract | 本省年雨量雖然充沛，但分佈不均勻，易造成水災濕害。玉米雖為耐濕性的作物，但是三天以上淹水，亦會造成傷害。在整個玉米生長期中，以種子發芽期對淹水濕害最敏感，其次是營養生長期V3至VS期，生殖生長期若遇淹水不發生倒伏，則傷害不大。淹水濕害造成產量減少，品質變劣。產量減少主要由於每穗子粒數的減少，粒重影響較少；主要原因是植株本身之光合產物供源潛勢（source potential）及積儲潛勢（sink potential）均因淹水而受到限制。
玉米幼苗期遭受淹水濕害，葉片生長立刻受到明顯的限制，老葉發生黃化，光合能力減退。此時幼苗有二種根系，種子根發生腐爛，不定根生長受抑制，但是淹水卻促進莖部較上節位不定根的萌發及生長，此種不定根具有通氣組織（aerenchyma）有利於植株耐濕性的產生。淹水濕害造成根系生長受抑制，直接影響對養分的吸收，特別是氮素。分析幼苗各部位氮素的濃度，發現地上部莖葉氮素明顯的減少，但根部氮素濃度並不低於對照植株，顯然根部的氮素無法轉運至地上部供給莖葉利用。淹水不僅限制根部氮素向上轉運，亦改變根部含氮化合物成分，NO3-N、NO2-N及膠基酸有累積增加現象。肢基酸中以tyrosine及alanine增加最多，而aspartic acid卻有減少的現象。分析氮素代謝的酵素活性，證實根部肢基酸含量增加，主要由於自行合成的增加，非由蛋白質分解而來。根部累積多量肢基酸在其生理上必有重要的意義，這種累積現象可能與玉米耐淹性有關。
Flooding was frequently occurred due to unevenly distribution of precipitation in Taiwan. Corn plants were more tolerant to flooding stress than other upland crops. Whereas, it was injured as the plants suffer from a 3-day flooding stress. The emergence of corn seed was highly susceptible to flooding during growth period, also the early growth stage (third leaf stage to fifth leaf stage) was sensitive to flooding. The damage was diminished as corn plants were entering repro- ductive stage except plants were lodged.
Corn yield was significantly decreased as the plants subjected to flooding stress, and yield reduction was mainly due to decrease in kernel number per ear. The decrease in yield was closely related to a lower source potential, as well as a lower sink potential.
Leaf growth was restricted, photosynthesis was declined and chlorosis by flooding treatment. While seminal roots was die and decay, adventitious roots growth was inhibited. However, flooding could promote the formation of adventitious roots at the upper nodes. This new formed adventitious roots have aerenchyma that contributed the tolerant to flooding stress.
And it was observed that nitrogen concentration decreased in the leaves, but not in the roots when the plants were subjected to flooding treatment. This means that there may have been a limited translocation of nitrogen out of roots to shoots.
Analyses of enzymes and components corresponding to nitrogen metabolisms showed that both increment of nitrite and free amino acids in the root tissue under flooding condition were expressed significantly. Amino acids accumulation could be due to both reduction of protein synthesis and increase of amino acid synthesis. Accumulation of tyrosine and alanine were expressed more significantly among amino acids in flooded corn roots. Accumulation of amino acids in roots may be play a regulatory role in alleviation of flooding injury. | en_US |
