Leaf Responses of Young Iron‐Inefficient Maize Plants to Sulfur Deprivation

Abstract

Hydroponically‐grown young iron (Fe)‐inefficient maize (Zea mays L.) plants were deprived of the external source of sulfate following an initial period when the sulfur (S)‐supply was sufficient. The effects of sulfate deprivation on leaf dry weight, dry weight to fresh weight ratio, chlorophyll fluorescence, SPAD reading, nitrogen (N) concentration, and Fe concentration of the lower leaves were monitored for 10 days. The patterns of leaf mass, area, chlorophyll content, and SPAD readings were analyzed according to leaf position. Decreased Fe concentration of leaf tissues was observed in all plants after the fourth day of the experiment, suggesting that this cultivar was Fe‐inefficient. An initial effect of short‐term S‐deprivation on leaves of young Fe‐inefficient maize plants was a lower Fe concentration of lower leaves in the second day. The fourth day of S‐deprivation experiment was a critical stage for the lower leaves, characterized by exhaustion of internal sulfate pools. After day 4, S‐deprivation affected both Fe‐ and N‐concentration of lower leaves. Nitrogen‐concentration remained stable and significantly less than that of the control plants and chlorosis became apparent. From the sixth day onwards, the lower leaves were characterized by decreased dry mass, higher dry weight to fresh weight ratio indicating less water content, less chlorophyll content although existing PSII systems were not affected, lower Fe concentration, and lower N concentration. Leaf development ceased, the fifth leaf did not emerge and the fourth one was less developed, the leaf mass to area ratio of the first three leaves was lowered, a progressive delay in the pattern of partitioning of chlorophyll content among leaves was observed, and the distribution of chlorosis intensity within the leaf blade was altered. Thus, after the sixth day the S‐starved plants experienced a complex constraint consisting of S‐depletion, Fe‐deficiency, and induced N‐deficiency.

Keywords:

• Sulfur nutrition
• Sulfur deprivation
• Iron‐inefficiency
• Zea mays
• Maize
• SPAD
• Chlorosis distribution

Acknowledgments

This work was supported by Framework V of the EU (QLRT‐2000‐00103). Rothamsted Research receives grant‐aided support from the Biotechnology and Biological Science Research Council (BBSRC) of the UK.