Rubber Formation in Hevea brasiliensis as affected by Light and Mineral Status

Abstract

De Haan and van Aggelen-Bot¹ reported that the amount of rubber per seedling (Hevea brasiliensis), in daylight, varied with the dry weight of the plant and that the amount of rubber did not diminish when the plant was kept in the dark. These findings have never been confirmed, and Teas² has recently suggested that rubber might be regarded as a food reserve in Hevea. Spence and McCallum³ concluded that rubber acted as a food reserve in guayule (Parthenium argentatum); but Bonner and Galston⁴ were unable to confirm this conclusion. If rubber can be regarded as a food reserve, its concentration in the tissues should, presumably, be affected by changes in mineral status which influence carbohydrate formation. This assumption may be partially correct as it has been shown⁵, for Hevea, that nutrient deficiencies may cause a diminution in the rubber concentration of stems and petioles in the earlier stages of growth, before the deficiency became sufficiently acute to cause a severe reduction in the total dry weight of the plant. This communication shows that the rubber contained in Hevea seedlings varied according to the dry weight of the plant and to the amounts of total carbohydrate and protein present, whether in the dark or in light, and in so far as these latter substrates were influenced by mineral status so also was the amount of rubber produced by the plant. However, these findings did not prove that rubber acted as a food reserve in Hevea as, under the ‘dark’ conditions of our experiment, severe starvation did not occur.