Influence of nitrogen sources on chloroplast development in wheat seedlings

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Abstract
The effect of different nitrogen sources (ammonium, nitrate or both ions together) on plastid development in dark‐grown and illuminated seedlings of wheat (Triticum vulgare L. cv. Yecora) has been investigated. Plastids of plants grown in ammonium showed even in the dark a larger internal membrane length, higher ribulose bisphos‐phate carboxylase activity and greater content of soluble proteins than plastids of plants grown in nitrate. After the first hour of illumination rudimentary thylakoids showing some joining points were observed in the ammonium plastids. After 10 h no prolamellar bodies were seen in the ammonium plastids, and the internal plastid membrane length was greater than in the other treatments. There was no light‐induced increase in protein synthesis after illumination for 1 h. After 10 h the increase observed in protein synthesis was not followed by a response in the enzyme activity in any of the treatments. After 20 h the lag in the induction of ribulose bisphosphate carboxylase ceased, the enzyme activity and soluble proteins being higher in the leaves of ammonium seedlings than in those from nitrate. From the correlation obtained between the ultrastructural electron microscope observations and the enzymatic studies, it appears that ammonium nutrition has a positive influence on the formation of the plastid membrane system and on the onset of photosynthesis and, consequently, on the development of chloroplasts.