Phytate related response of maize seed to phosphorus and temperature.
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Date
2006
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Abstract
The aim of the study was to determine the effect of day/night temperatures (22/l6°C,
2712l oC and 33/27°C) and phosphorus levels (0, 0.12 and 1.2g per 20 kg soil) on seedling
establishment and seed viability during three stages of seed development (15, 22 and 33
days after flowering) for seed of normal and quality protein maize cultivars. Soluble
carbohydrate accumulation and mineral element content were determined using
environmental scanning electron microscopy (ESEM) in relation to seed phytate levels
and seed germination capacity at different stages of development. Leaf emergence rate
and plant height during seed development were significantly (P < 0.05) influenced by
temperature and phosphorus nutrition. Phosphorus in seed is stored primarily in the form
of phytic acid, also known as phytate. Accumulation of phytate takes place during
maturation phase of seed development. Phosphorus nutrition and temperature also caused
a.significant (P < 0.05) increase in seed germination at all stages of seed development.
Furthermore, phosphorus nutrition and temperature influenced occurrence of soluble
carbohydrates in seeds. Myo-inositol, the sugar alcohol that forms the basic structure of
phytate, was increased by P nutrition and increasing growth temperature. Whereas, QPM
maize was generally found to perform poorly than normal maize, with respect to phytate
content, seed germination and seedling establishment, both cultivars displayed the same
responses to phosphorus nutrition and temperature. In both cultivars, globoids, the sites
of phytate synthesis and storage, were found only in the embryonic axis. Subsequently,
there were significantly low levels of mineral elements (P, Mg and K) found in the
endosperm, compared with embryonic axis. This finding suggested that the embryonic
axis plays a major role in seed performance, through its effects emanating from phyate
metabolism. Myo-inositol plays a role in membrane biogenesis during stress conditions
such as temperature by maintaining the integrity of the cell wall and minimizes the
leaching of cations essential during germination.
Myo-inositol, although it occurs in small concentrations, could be used to indicate seed
quality in maize, because its accumulation was found to be associated with enhanced
phyate levels and better seed germination in a wide range of temperatures. Low vigour
seeds are associated with high electrolyte leakage during imbibition. Mineral elements
form a significant portion of the imbibition leachate, which causes seeds to lose nutrients
for early seedling growth. This study provided evidence that phosphorus nutrition can
alleviate poor seed vigour of maize by improving phytate levels.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.
Keywords
Maize--Seeds., Maize--Seeds--Viability., Maize--Seedlings., Maize--Seedlings--Evaluation., Seeds--Development., Seeds--Growth., Maize--Effect of temperature on., Phosphorus--Physiological effect., Germination., Theses--Crop science.