Studies on the mechanisms of reduction of stem elongation by cold water irrigation in tomato seedlings.

• Main Authors: Yung-Wei Sun, 孫永偉
• Other Authors: Woo-Nang Chang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/65963422733066146878

博士 === 國立中興大學 === 園藝學系 === 92 === The purposes of this study were to establish the cold-water irrigation system for plug-seedlings production, and to reveal the possible mechanisms by which cold-water mediated the reduction of stem elongation in tomato seedlings. The shortest seedlings were found in the seedlings irrigated with the lowest or highest water temperature. However, highest stem strength and seedling index were only found in the seedling irrigated with the 5℃ water. Decrease in the length of first internode was primarily responsible for the shortening seedling by cold-water irrigation. Irrigation of cold water in the morning (8:00) or evening (16:00) showed the best results in shortening seedling. After the cold water irrigation, the soil temperature drop to minimum within 60 to 90 sec, and recovered to the room temperature after 60 min. Longer period of cold-water irrigation and lower the cold-water temperature resulted in shorter seedlings. Significant reduction in the plant height and increases in the seedling index and chlorophyll contents were found in the seedlings irrigated with cold water. Among five major groups of plant hormones, only GAs and ethylene could promote or inhibit the stem elongation of tomato seedlings, respectively. Increase in the seedling index and chlorophyll contents by cold-water irrigation was inhibited by GAs application. Stem elongation induced by room-water irrigation was inhibited by ethylene application, but seedling index and chlorophyll contents were decreased. Furthermore, the PP333 and STS were applied to abolish the actions of GAs and ethylene, respectively. The results indicated that the PP333 could mimic the actions of cold-water on tomato seedlings for reduction of stem elongation, and increases in the seedling index and chlorophyll contents, but STS was fail to abolish the action of cold-water. The results indicated that the significant decrease in the cell length of first internode was found in the tomato seedlings irrigated with cold water (5℃), and there were no changes in the cell numbers and cell width. Both pp333 (10 ppm) and ethephon (53 ppm) applications can cause the reduction of stem elongation of tomato seedlings at room temperature. The cellular morphological chacters, such as cell length, the ratio of cell length to width, stomata density, and compact palisade tissue in PP333-trteaded seedlings were similar to those in cold-water irrigated seedlings, but different from those in the ethephon-treated seedlings. Increases in cell length, the ratio of cell length to width, stomata density, and compact palisade tissue were found in the 5℃+GA-treated, 25℃+PP333+GA-treated, and cold-water irrigated seedlings, but not in the 5℃+STS-treated seedlings. The expressions of 3β-hydroxylase and 20-oxidase genes were higher in the cold-water irrigated seedlings than in the room-temperature irrigated seedlings, but declined after addition of GAs. Both PP333 and ethephon application could cause reduction of stem elongation in tomato seedlings, but had the different patterns in induction of the expressions of 3-hydroxylase and 20-oxidase genes. The results of effects of STS (silver thiosulphate) on the expression of 3β-hydroxylase, 20-oxidase, ACC synthase, and ACC oxidase genes implied that there were no differences in the ethylene metabolism between cold-water irrigated and room-temperature irrigated seedlings. The reduction of stem elongation was found in the Nr, Pearson, VFN8, and Money maker, but not in the epi and gib-3 after 3-weeks of cold-water irrigation, i.e. the inhibition of stem elongation caused by cold-water was not shown in the situations of ethylene over-expression (epi) and GA shortage (gib-3). Except gib-3, decreases in the cell length were found in all other varieties (lines). Increases in the expression of 3β-hydroxylase and 20-oxidase genes were found in all varieties (lines) after cold-water irrigation, but not the expressions of ACC synthase and ACC oxidase genes. In responding to the increasing doses of GA, increases in plant height, and decreases in the transcripts of 3β-hydroxylase and 20-oxidase genes were found in gib-3, but there were no differences in the transcripts of ACC synthase and ACC oxidase genes. In conclusion, cold-water irrigation system for the production of plug-grown seedlings could be useful in the commercial application. Decrease in the cell length of first internode was primarily responsible for the reduction of stem elongation induced by cold-water irrigation. It is suggested that blocking GA metabolism, not ethylene, may be involved in the events of cold-water mediated reduction of stem elongation in tomato seedling.