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Abstract
Iron chlorosis‐like symptoms developed in the terminal leaves of susceptible bean (Phaseolus vulgaris L. ‘Astro') plants when grown in growth chambers containing low pressure sodium (LPS) lamps that are deficient in UV and blue wavelengths. Plants grown under broad‐band radiation, provided by cool white fluorescent lamps, did not develop chlorosis. Ultrastructural and metabolic investigations examined the progress of chlorosis in leaves of plants exposed to nutrient end radiation stress under LPS lamps. Addition of full‐strength Hoagland's #1 nutrient solution or Peter's* 20–20–20 fertilizer to plants grown under LPS lamps resulted in the degradation of maturing chloroplasts in the terminal leaves. After the starch reserves were depleted, the internal membrane system degenerated. Well‐formed grana, characteristic of normal chloroplasts, were degraded, giving rise to spherical membrane structures. Chlorophyll and protein were lost and granular accumulations formed in the chloroplasts. This paper discusses the stability of the chloroplasts and mesophyll under LPS radiation and evaluates the ability of the leaves to regreen when the plants are subjected to favorable radiation and nutrient conditions. Soil application of urea and EDU, along with foliar application of sucrose, promoted regreening of the chlorotic leaves. It was concluded that chlorosis in LPS‐grown plants resulted from photodegradation of the more mature chloroplasts rather than from inhibition of lamellar development due to Fe deficiency.