Effects of root temperature on iron stress responses

Abstract

Pepper plants (Capsicum annuum L.) were transferred to all NO₃ ^- N nutrient solution, lacking Fe, in tubes maintained in water baths held at 15, 20, 25, 30 and 35^°C with air temperature at 28^°C day and 25^°C night. Nutrient solution pH incresed initially at all temperatures as it did in plants having iron, but did so slightly more rapidly at 30^° and least rapidly at 15^°C. With the onset of iron stress, decreases in nutrient pH were most pronounced at 30^°C, moderate at 25^°C and not evident at 15, 20, and 35^°C over 12 days. Riboflavin excretion from roots preceded pH decreases by several days, but amounts increased greatly with pH decreases. The maximum riboflavin from plants at 30^°C root temperature exceeded that for plants at the lowest root temperature by more than 2000 fold. Root iron reduction increases were pronounced and moderate at root temperature of 30^°C and 25^°C, respectively, and negligible at other root temperatures. These reduction increases paralleled initial riboflavin excretion. Root and shoot fresh mass were maximal at 30^°C root temperature and total mass exceeded that from plants at 15^°C root temperature by about 2 fold, whereas the differential in secondary root mass was larger. Chlorosis was most pronounced at 25, 30, and 35^°C root temperatures.