The Role of Boron in the Translocation of Sucrose.

The essentiality of boron for higher plants was demonstrated (1) in 1910 and extensively verified in the two succeeding decades. Since then a voluminous literature has accrued concerning the anatomical, morphological, and biochemical alterations of boron-deficient plants. Inasmuch as they are not pertinent to the following report, many of the specific or general roles that have been postulated for boron will not be discussed. By their omission the authors do not mean to imply that boron has no role or roles other than the one presented since, for example, the inverse relationship between boron level and per cent. moisture in plant tissues has been firmly established by MIINARIK and SHIVE (15) and others. To date, however, no one has demionstrated the exact role or mode of action of boron in higher plants. It is the purpose of this report to offer evidence for one role of boron. In view of the well-known reaction of the borate ion with OH-rich comnpounds and its recent application in the borating of sugars in order that they may be separated on ion-exchange columns (14, 18), the authors conceived and tested an hypothesis as to one essential role of boron in plants. The hypothesis is that boron combines with sugar to form a sugar-borate coiiplex (ionizable) whichl is translocated withi greater facility than are nonborated, non-ionized sugar molecules. Inasmuch as most studies have indicated that sucrose does not move readily through cellular membranes, the work reported herein was limited to sucrose and the effect of a few (5 to 10) parts per million of boron on its translocation. According to ZITTLE (26) the borate ion reacts most strongly with OH-rich compounds in which there are two OH groups in the cis position. Althouglh the structure of sucrose does not fulfill this requiremiient, there is ample evidence that there is a reaction with sucrose and that it involv es the trans-1,2-diol groups. Further (26), it is suggested that the following structure is formiied with sucrose