Light‐induced reduction of FE3+as related to causes of chlorosis in cotton

In growth chambers, cotton (Gossypium hirsutum L. genetic selection ‘M8') was grown in a synthetic growth medium under four light regimes: low pressure sodium (LPS), LPS + Incandescent (Inc), cool white fluorescent (CWF) and CWF + Inc lamps at 22 C under LPS lamps. Less chlorosis developed at 26 C than at 22 C and less under LPS + Inc than under LPS lamps. All plants were green under CWF and CWF + Inc light. Green and chlorotic plant tissue contained about the same concentrations of Fe. The proposed hypothesis was that chlorotic tissue’ contained less Fe2+ than green tissue. Chlorotic leaves treated with FeSO4 turned a green color. Enough CWF + Inc light passed through an intact leaf to reduce Fe3+ to Fe2+ in vitro. Also in vitro, Fe3+ was reduced by CWF, by Inc, but not by LPS light. The amount of Fe3+ reduced during an illumination period was directly proportional to the quantity of light used. In vitro, citrate and malate enhanced Fe3+ reduction, whereas phosphate, pyrophosphate, OH‐, Cu2+, Ni2+, Mn2+, Zn2+, and F‐ all inhibited Fe3+ reduction by light. Orthophosphate was about 8 times as effective as organic P in decreasing Fe3+ reduction. Citrate largely alleviated the inhibitory effects of Pi and pH (up to pH 6). The data also provide a possible explanation of a role for many of the elements known to induce or aggravate Fe chlorosis (inhibit Fe3+ reduction). Quantity and quality of light apparently play key roles in plant growth as related to reduction of Fe3+ to Fe2+ in plant tops.