Investigation of atypical germination changes during accelerated ageing of pea seeds

Abstract

Pea seeds with initial germinability of 100, 82 and 56% were subjected to accelerated ageing for 16 days at 40°C and 85% relative humidity (RH). Upon ageing of seeds with initial germinability of 82 and 56%, multiphasic changes in germination (production of normal seedlings) were observed: after 5 or 7 days of ageing, germinability decreased to 72 and 22%, respectively, but after 8 or 10 days it rose to 92 and 60%, respectively. Prolongation of ageing led to deterioration of both germinability and seed viability. When the seed sample with initial germinability of 56% was pre-treated for three days at 20°C and 85% RH (during which the moisture content (MC) reached 15% fresh weight (FW)) before being subjected to accelerated ageing, the initial decrease and subsequent increase of germination were observed 3 days earlier. When the seed lot with germinability of 82% was subjected to controlled ageing at 20% MC, only a consistent steady decline in germination was observed. A similar decline was also observed during accelerated and controlled ageing of seeds with almost 100% germinability (MC 18, 20, 21 and 22%). Measurement of room temperature phosphorescence (RTP) of seeds, was used to divide the sample of air-dry low-germination seeds into three fractions (sub-lots): viable seeds of fraction I (produced normal seedlings), viable seeds of fraction II (produced abnormal seedlings) and dead seeds (fraction III). Changes in germination during ageing were due to changes in the proportion of seeds occurring in fractions I and II. Fraction II seeds differed from fraction I by characteristically higher rate of water uptake during the imbibition. However, the high rate of imbibition was not caused by changes in seed-coat permeability of fraction II seeds. After slowing seed imbibition by PCMB (a mercurial closing aquaporin water channels), seeds of fraction II produced normal seedlings and germinability increased. It is proposed that the atypical increase in germination capacity during accelerated ageing was due to lower permeability of cell membranes for water.