Further Investigations on the Relation of Photo Period to the Boron Requirement of Plants

Abstract

Plants of cockle-bur grown without B and exposed to short days fruited and showed no deficiency symptoms; those grown in long days without B remained vegetative and displayed external and anatomical signs of B deficiency. Plants displaying B deficiency symptoms showed tissue disorganization resulting from abnormal cambial activity, proliferation and enlargement of some of the cells of the cambial zone. An induction period of 10 days, after which the plants were transferred to long days, reduced the expression of B-deficiency symptoms. With an induction period of 10 days, cambial activity had decreased so that the cellular abnormality associated with B deficiency did not occur. Soybean var. Biloxi is a short-day plant and resembles cocklebur in its response to B deprivation. Pagoda soybean becomes fruitful at an early stage in both short and long days so that deficiency symptoms were not evident in a culture without B in either short or long days. Tomato and sunflower are day-neutral plants and flower much later than cocklebur. The cambium remains active longer in these plants, permitting the lack of boron more time to show its effect. With a minus B supply, deficiency symptoms were apparent in both short and long days. Buckwheat is also a day-neutral plant. It flowers at a very early stage of development, especially at a short photoperiod. Deficiency symptoms were not evident in short days; however, in long days maturation of tissues was less rapid and slight symptoms of deficiency were apparent in plants grown without B. Apparently the decrease in cambial activity associated with the rapid flowering habit of some plants accounts for reduction in severity of boron-deficiency symptoms.