Effect of acidic polypeptides on aluminium toxicity in tube growth of pollen from tea (Camellia sinensis L.)

Pollen of tea (Camellia sinensis L.) was germinated in liquid culture and the rate of extension growth of the pollen tube was used to study the effect of the acidic polypeptides poly-L-aspartic acid and poly-L-glutamic acid on the toxic effects of Al on tip growth. Tube extension was inhibited as much as 70% by 10 gmM Al over 20 h of growth. Citric acid at a molar ratio of 3:1 was able to reduce the inhibition to 40%. However, poly-aspartate was much more effective, being able to reduce inhibition to about 50% at a ratio of 1:1 (20 μM poly-L-aspartate:20 μM Al, the poly-aspartate molarity being calculated using the molecular weight of the individual aspartate residue). Growth could be completely protected from toxic effects of Al at a ratio of 10:1. Similar results were found with the same concentrations of poly-L-glutamate. The polypeptides alone had no effect on growth. It is probable that the polypeptides bind Al. Since a requirement for Ca2+, and the involvement of calmodulin, are implicated in pollen tube growth, the polypeptides may prevent Al from interfering with Ca2+ transport, or from binding to calmodulin.