GENE EXPRESSION AND INTERNAL FEEDBACK REGULATION OF ETHYLENE BIOSYNTHESIS IN FRUITS AND VEGETABLES

。番茄果实发育成熟过程中乙烯生物合成相关基因的表达及其内部反馈调控。番茄果实跃变前期乙烯可能通过LE-ACS1A和LE-ACS3的组成性表达和负反馈调控的LE-ACS6基因与预先存在的LE-ACO1和LE-ACO4mRNAs共同调控，在番茄果实发育和成熟过程中可能转移到LE-ACS2、LE-ACS4、LE-ACO1和LE-ACO4mRNAs的大量积累。从系统1到系统2的这种乙烯产生的转变可能与NRmRNA的积累水平有关。从非跃变型黄瓜果实中克隆了5个编码ACC合成酶和ACC氧化酶的基因片段。然而，这些基因在核苷酸序列上与跃变型甜瓜果实中的相应基因高度同源，CS-ACS1基因在成熟的黄瓜果实中不表达。CS-ACS1为创伤诱导基因，CS.ACS3为生长素诱导基因。在甜瓜果实中，不同品种果实乙烯形成能力的差异源于果实自然成熟过程中CME-ACS1基因的表达以及外源乙烯的响应。MA-ACS1基因是香蕉果实中与果实成熟过程有关的基因，受外源乙烯的诱导。随着MA-ACS1mRNA积累量的增加，乙烯释放量急剧增加，并出现一个尖锐的峰值，随后迅速下降。这个乙烯产生的尖锐峰值伴随着体内AGO氧化酶活性的尖锐峰值。然而，MA-ACO1转录本的水平从开始进入更年期到完全成熟阶段一直保持在较高水平。这种酶活性和AGO氧化酶基因表达之间的差异，至少部分是由于成熟过程中酶的辅助因子抗坏血酸和亚铁含量减少所致。

. Expression and internal feedback regulation of the genes related to ethylene biosynthesis during development and ripening in several fruits were investigated.In tomato fruit, the preclimacteric system 1 ethylene was possibly mediated via constitutively expressed LE-ACS1A and LE-ACS3 and negatively feedback-regulated LE-ACS6 genes with preexisting LE-ACO1 and LE-ACO4 mRNAs, At the onset of the cimacteric stage, it may shift to system 2 ethylene, with a large accumulation of LE-ACS2, LE-ACS4, LE-ACO1, and LE-ACO4 mRNAs as a result of a positive feedback regulation. This transition from system 1 to system 2 ethylene production might be related to the accumulated level of NR mRNA.Five cDNA fragments encoding ACC synthase or ACC oxidase were cloned from cucumber fruit, a nonclimacteric type. Nevertheless., these were highly homologous in nucleotide sequences to the corresponding genes in melon fruit, a climacteric type, CS-ACS1 gene was not expressed in the ripening cucumber fruit. CS-ACS1 was a wound-inducible gene and CS.ACS3 was an auxin-inducible one. In melon fruit, the difference in the ethylene-forming capability among cultivars resulted from the expression of CMe-ACS1 mRNA during natural fruit ripening and in response to exogenous ethylene.MA-ACS1 was the gene in banana fruit related to the ripening process and was inducible by exogenous ethylene. At the onset of cimacteric, ethylene production increased greatly with a sharp peak concomitant with an increase in the accumulation of MA-ACS1 mRNA and then decreased rapidly. This sharp peak of ethylene production was accompanying a sharp peak of in vivo AGO oxidase activity. However, the level of MA-ACO1 transcripts remained high from the onset of climacteric to the fully ripe stage. This discrepancy between enzyme activity and gene expression of AGO oxidase was, at least in part, due to reduced contents of ascorbate and ferrous, cofactors of the enzyme, during ripening.