Acid accumulation on detached fruits of tomato

Abstract

This study was made to investigate the possible ability of acid production and accumulation of fruits themselves by using detached fruits of tomato (cv. Fukuju No. 2), and to make clear the role of base or potassium in regulating the acid accumulation.Tomato fruits were detached from plants at several stages and were kept in the room controlled at 20°C. The total acidity of detached fruits increased steadily when detached at the stages of green fruits. In the case, however, that the fruits were detached at the turning, the decrease of total acidity was found. The titratable acidity of detached fruits showed the change similar to that of total acidity. Combined acidity, on the other hand, made comparatively small change.For the experiment on the role of potassium (K) or base, i. e., combined acidity (C), fruits were detached on 35 days after flowering from the plants grown under different levels of potassium fertilizer and were kept in 20°C room until turning. On the fruits on vine 35 days after flowering, the linear relations were observed between total acidity and potassium content or combined acidity, i. e., T=1.19K+1.72, T=1.44C+0.79, respectively. Such linear relations were found also on fruits which were detached on 35 days after flowering and kept in 20°C room until turning, i, e., T=1.90K+1.95, T=2.22C +0.93, respectively.These liner relations mean that the increment of total acidity (ΔT) after detached until turning was dependent on potassium content or combined acidity. Then, supposing that there was no change on potassium content or combined acidity after detached, the increment of total acidity will be expressed as follows, ΔT=0.71K+0.23 or ΔT=0.78C+0.14.From these results, it was suggested that tomato fruits which were detached from plants at green stages were able to synthesize and to accumulate acids. Besides, the fact that the detached fruits can accumulate acids was thought to be based on the following two conditions, namely (a) the ratio of acid to base, i. e., the ratio of total acidity to combined acidity is maintained at a certain value if the developmental stage of fruits is the same, and (b) the ratio of acid to base becomes higher as the time after detached elapses, during which the physiological development on detached fruits may proceed.