Mineral elements and embryo development in barley
This work describes the accumulation of a number of essential mineral elements during embryo development in barley together with the effects of variation in their supply on embryogenesis.The mineral elements investigated were potassium, magnesium, calcium, iron, copper and manganese, and a rapid wet ashing procedure, coupled with flame and flameless atomic absorption spectroscopy was devised for their determination in barley embryos and endosperms. Recoveries of all the elements studied from embryo and endosperm samples were goodAlthough the accumulation of all these mineral elements was found to be related to embryo growth, the concentrations (w/w) were much higher at earlier, rather than later, stages of development. For example almost half the calcium content of the mature embryo was assimilated by 21 days after anthesis.The patterns of mineral ion accumulation in four barley cultivars were similar, although the concentrations (w/w) of calcium were rather higher in the cultivar Julia.Variation in the magnesium supply led to higher manganese and calcium, and lower magnesium concentrations (w/w), in the developing embryos. Manganese did not totally compensate for lack of magnesium and chlorosis was observed in seedlings from magnesium 'deficient' seeds. Only at later stages of development did the endosperm become deficient in magnesium.The withdrawal of both magnesium and manganese from the rooting medium resulted in low magnesium levels in both the embryos and endosperms.As before, the embryo manganese levels increased, but in this case the endosperm manganese levels fell. Potassium levels in both cases were unaffected.In vitro embryo culture was also used to investigate the effects of variation in the mineral supply on embryo development. Norstog's Medium II (0.2 M sucrose) satisfactorily supported the growth of barley embryos in culture, as assessed by a number of criteria including embryo ultrastructure and external morphology. Magnesium withdrawal resulted in a significant increase in embryo size. Whether this was related to cell number or cell size was not determined.The results are discussed both in relation to the biochemistry and physiology of embryogenesis and to the possible role of the endosperm in the nutrition of the growing embryo.