PHYSIOLOGICAL ASPECTS OF LOW TEMPERATURE SEED GERMINATING ABILITY IN TOMATO (LYCOPERSICON ESCULENTUM MILL.)
Abstract
The inherent ability of tomato seed to germinate at low temperature is negatively correlated with oleic acid content and positively correlated with linoleic acid content in dry seeds of parent and partially isogenic F(,5) lines with varying low temperature germinating abilities. Fatty acid composition does not change with time of incubation at 10(DEGREES)C. The proportion by which linoleic acid is higher in the cold germinating parent PI341985 (CG) over the non-cold germinating cultivar Centennial (NCG) is roughly the same as the amount by which oleic acid is lower, suggesting that the primary effect of genes controlling cold germinating ability is to promote or regulate a more extensive desaturation of oleic acid into linoleic acid during seed development. Lower unsaturation of membrane systems in NCG would mean that membrane phase changes may occur at 10(DEGREES)C in NCG, but not in CG, impairing the permeability properties of the former. Pre-incubation of CG and NCG in water at 25(DEGREES)C for up to 24 hours prior to incubation at 10(DEGREES)C failed to alter the relative performance of these lines at low temperature. Activated carbon improved cold germination throughout the range of cold germinating abilities, but its effect was more pronounced in lines with low germination indices (GI) at 10(DEGREES)C than in lines with high GI. Nonetheless, the improvement was not sufficient to bring the cold germination of lines with low GI to the level of non-carbon treated lines with high GI. The peroxidase activity increase observed in CG during incubation at 10(DEGREES)C appears to represent a secondary effect of genes regulating low temperature germination. Peroxidase activity in CG and NCG is unaffected by activated carbon. The possibility that peroxidase, along with catalase and NAD(P)H:quinone oxidoreductase, may be part of a dormancy-breaking mechanism leading to activation of the Pentose Phosphate (PP) Pathway was investigated. Results were inconsistent with the hypothesis that H(,2)O(,2), spared from decomposition by inhibition of catalase, would then be metabolized via the enzymes peroxidase and NAD(P)H:quinone oxidoreductase to oxidize reduced NADPH for use in the PP pathway. Isocitritase activity was detected in CG and NCG seeds incubated at 10(DEGREES)C and 25(DEGREES)C, but the differences in cold germinating ability between these lines cannot be explained by the ability of CG to utilize fats earlier than the NCG cultivar. However, the slightly higher isocitritase activity shown by CG over NCG may be responsible for the higher reducing sugar contents observed in the CG following 10 days of incubation at 10(DEGREES)C. Soaking CG and NCG seeds in the presence of inhibitors of nucleic acid or protein synthesis, or in the presence of all possible combinations of different levels of ABA, GA(,3) and kinetin failed to negate the genetic difference in low temperature germinating ability between the lines. Ability of tomato seeds to germinate at low temperatures is not a cold-induced phenomenon, and appears to be related to fatty acid composition of cell membranes, which is predetermined in the dry seed. The primary effect appears to be the desaturation of oleic acid into linoleic acid which takes place during seed development. The extent of this desaturation is closely correlated with cold germinating ability of the line. Other observed differences between CG and NCG appear to represent secondary effects.
Degree
Ph.D.
Subject Area
Botany
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