Effects of seed ageing on early post-germination root extension in maize: a spatial and histological analysis of the growth-zone

The effects of deterioration of maize (Zea mays L. cv Jubilee) seed on the spatial distribution of root growth, and its cellular basis, was investigat ed. Seed (caryopses) of maize were artificially aged at 45 degrees C and 18 % seed moisture content for 30 h. This regime reduced seed vigour, but had only a small effect on the final % germination. All experiments on root gro wth were conducted between 72 and 75 h after imbibition using cohorts of ag ed and unaged seed which germinated between 24 and 48 h. Seed ageing reduce d the extension rate of primary roots by 31%. Marking experiments revealed that this was the result of a lower maximum relative elemental growth rate, a premature deceleration in rate and a shorter growth-zone. Cell prolifera tion in the cortex was examined. Ageing reduced the mitotic index throughou t the meristem, which was slightly smaller compared to controls. Cell doubl ing time was increased by ageing, indicating a slower rate of cell producti on. The profiles of cortical cell length were comparable for roots from age d and unaged seed over the apical 5 nun, but mature cell length was reduced , suggesting that effects of ageing on cell expansion were greater than tho se on cell division.