INVOLVEMENT OF ENDOMANNANASE IN THE CONTROL OF TOMATO SEED-GERMINATION UNDER LOW-TEMPERATURE CONDITIONS

The cause of differences in germination rates in a cold-tolerant tomat o line (PI341988), a control line (UC82B), and six progeny lines stemm ing from crosses and backcrosses between the two parent lines was inve stigated. Pursuant to earlier work showing that differences in germina tion ability at 12 degrees C are due to the barrier imposed by the end osperm layer, we analysed the activity of cell-wall-hydrolysing enzyme s extracted from these lines. A significant increase in endomannanase activity was found in plant line PI341988 prior to germination at 12 d egrees C. Extracts of PI341988 seeds that had imbibed at either 12 or 25 degrees C exhibited higher endomannanase activity than their counte rparts from plant line UC82B. Moreover, a positive relationship was fo und between germination ability at low temperature and endomannanase a ctivity in the six progeny lines. Analysis of endomannanase activity i n sub-regions of the seed indicated that the increase in activity prio r to germination was higher in the micropylar endosperm cap than in th e rest of the seed. Exogenous application of mannanase originating fro m soil-borne bacteria increased germination rates under both moderate and low temperature conditions. Cellulase (endo-1,4-beta-glucanase) ac tivity was also found to be higher in plant line PI341988. However, th e activity of this enzyme probably increases after germination and it is therefore not considered as a key enzyme controlling germination at low temperatures. (C) 1995 Annals of Botany Company