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Photoassimilates Distribution in Micropropagated Apple Plants During and after Water Stress

Author: DaiZhanWu
Tutor: LiShaoHua
School: China Agricultural University
Course: Pomology
Keywords: Mulus demestica Borkh. 14C-Photoassimilate Distribution Water Stress Rewatering After Effect
CLC: S661.1
Type: Master's thesis
Year: 2005
Downloads: 154
Quote: 1
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Abstract

The effect and after-effect of water stress on distribution of photoassimilates, fixed at different times during and after water stress, were investigated in one-year-old micropropagated ’Gala’ apple （Malus domestica Borkh.） plants by feeding mature leaves with ¹⁴CO₂. Plants grown in Hoagland nutrition solution in a growth chamber were subjected either to prolonged water stress （PWS）, induced by polyethylene glycol （PEG6000） at moderate intensity （18% W/V） for 15 days or to moderate stress for three days and then transferred to non-PEG solution for 12 days recovery （RAWS） compared with plants under normal water conditions （CK）. Specific radioactivity （SRA）, percentage distribution value and distribution coefficient （K） were used to evaluate the absolute amount of photoassimilates in organs, relative distribution among sinks, and the competitive sink strength, respectively. CO₂ exchange rate of source leaves in PWS plants, as estimated by the total radioactivity in the whole-plant, was significantly reduced by water stress 24 h after initiating treatments and there was a five-day lag in complete recovery after removing water stress. This source limitation eventually led to reduced SRAs of all the sink organs in PWS at the advanced phase of water stress. The percentage of ¹⁴C-photoassimilate retention in the labeled leaves was significantly increased in PWS plants over CK plants, and the differences increased between PWS and CK with prolonged water stress. The longer plants were subjected to water stress, the greater the proportion of ¹⁴C-assimilates retained in the leaves. At the end of the experiment, the retention of ¹⁴C-photoassimilate in PWS leaves increased to about 75%, 1.5 times of CK leaves. Shoot apex and fine root responded most quickly （only one hour after initiating water stress） than other organs to water stress in different pattern, resulting in decreased distribution coefficient （K）, percentage distribution value and SRA in shoot apex （about 26%, 19% , and 22% of CK） but increased the parameters in fine root of PWS plants compare with CK. This suggests that shoot apex is most sensitive to water stress and the ¹⁴C-photoassimile distribution likely shifts from above-ground to root, being benefit to maintaining root growth and tolerance to water stress. Furthermore, the changes of ¹⁴C distribution in source and sink organs in PWS plants indicated that not all photoassimilates, fixed under different status of water stress, shared the same distribution pattern, but varied with the plant physiological status. On the other hand, the percentage of ¹⁴C-photoassimilate distributed into phloem declined linearly with increased retention in the labeled leaf, confirming that the phloem was just a pathway for transporting assimilates and the higher K did not signify a stronger sink strength of water-stressed phloem. The compensation effect of water stress only was observed in the percentage distribution values in fine roots of RAWS plants, which kept significantly higher than that of CK during rewatereing. However, there apparently was an after-effect of water stress, as revealed by the delayed recovery of almost all of the three parameters in RAWS plants.

Photoassimilates Distribution in Micropropagated Apple Plants During and after Water Stress

Abstract

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