DIFFERENTIAL REGULATION OF POLYGALACTURONASE AND PECTIN METHYLESTERASE GENE-EXPRESSION DURING AND AFTER HEAT-STRESS IN RIPENING TOMATO (LYCOPERSICON-ESCULENTUM MILL) FRUITS
V. Kaganzur et al., DIFFERENTIAL REGULATION OF POLYGALACTURONASE AND PECTIN METHYLESTERASE GENE-EXPRESSION DURING AND AFTER HEAT-STRESS IN RIPENING TOMATO (LYCOPERSICON-ESCULENTUM MILL) FRUITS, Plant molecular biology, 29(6), 1995, pp. 1101-1110
The effects of extended heat stress on polygalacturonase (PG; EC 3.2.1
.15) and pectin methylesterase (PME; EC 3.1.1.11) gene expression at m
RNA, protein and activity levels in ripening tomato fruits were invest
igated. Steady state levels of PG mRNA declined at temperatures of 27
degrees C and above, and a marked reduction in PG protein and activity
was observed at temperatures of 32 degrees C and above. Exogenous eth
ylene treatment did not reverse heat stress-induced inhibition of PG g
ene expression. Transfer of heat-stressed fruits to 20 degrees C partl
y restored PG mRNA accumulation, but the rate of PG mRNA accumulation
declined exponentially with duration of heat stress. Heat stress-induc
ed inhibition of PME mRNA accumulation was recoverable even after 14 d
ays of heat stress. In fruits held at 34 degrees C, both PG and PME pr
otein and activity continued to accumulate for about 4 days, but there
after PG protein and activity declined while little change was observe
d in PME protein and activity. In spite of increases in mRNA levels of
both PG and PME during the recovery of heat-stressed fruit at 20 degr
ees C, levels of PG protein and activity declined in fruits heat-stres
sed for four or more days while PME protein and activity levels remain
ed unchanged. Collectively, these data suggest that PG gene expression
is being gradually and irreversibly shut off during heat stress, whil
e PME gene expression is much less sensitive to heat stress.