Influence of cobalt and iron on photosynthesis, chlorophyll, and nutrient content in regreening chlorotic tomatoes and soybeans

Abstract

Iron‐efficient and ‐inefficient tomatoes (T3238 PER and T3238 fer, respectively) and soybeans (A7 and T203, respectively) were grown in nutrient solution culture for nine and seven days with four Pe‐Co treatments (0,0; 1,0; 1,1.2; and 0,1.2 mg/liter Pe and Co, respectively) . Both Pe‐eff icient and ‐inefficient cultivars exhibited Pe‐ and Co‐induced chlorosis, but the efficient PER cultivar was least susceptible to both stresses. Cobalt generally decreased net photosynthesis (Pn), chlorophyll, and foliar iron in either the presence or absence of Pe.

After nine and seven days of growth in the above treatments (tomato and soybean, respectively), new solutions were introduced to all of the above treatments, and 1 mg Pe/liter was added to three treatments to study regreening (designated 0,0+; 0,1.2+; 1,1.2+); the original control treatments (0,0; 1,0) continued without additional iron. Recovery of Pn and chlorophyll from added Pe was observed in all cultivars for the 0,0+ treatment, was variable among cultivars for the 1,1.2+ treatment, and was observed only in PER tomato for the 0,1.2+ treatment. Any influx of Pe during the regreening phase accumulated primarily in the leaves in the absence of Co (0,0+) and in the roots in the presence of Co (0,1.2+ and 1,1.2+). Iron‐stress responses (pH and reductant) were apparent only with 0,0 treatment for A7 and PER and were eliminated by adding Pe (0,0+).

Key words:

• Cobalt
• Iron‐efficient
• Iron‐inefficient
• Leaf iron
• pH
• Reductant
• Root iron