Differential effects of aluminum on in vitro primary root growth, nutrient content and phospholipase C activity in coffee seedlings (Coffea arabica).

Coffea arabica is a woody species that grows in acid soils, where aluminum is available and may affect growth and productivity. To determine the effect of aluminum on primary root growth of C. arabica cv. Typica, seedlings were exposed over 30days to different concentrations of AlCl3 (0, 100, 300 and 500μM) in vitro. The aluminum effect on primary root growth was dose-dependent: low aluminum concentrations (100 and 300μM) stimulated primary root growth (6.98±0.15 and 6.45±0.17cm, respectively) compared to the control (0μM; 5.24±0.17cm), while high concentrations (500μM) induced damage to the root tips and inhibition of primary root growth (2.96±0.28cm). Aluminum (100μM) also increased the K and Ca contents around 33% and 35% in the coffee roots. It is possible that aluminum toxicity resides in its association with cell nuclei in the meristematic region of the root. Additionally, after 30days of treatment with aluminum, two different effects could be observed on phospholipase C (PLC) activity. In shoots, aluminum concentrations ≥300μM inhibited more than 50% of PLC activity. In contrast, in roots a contrasting behavior was determined: low (100μM) and toxic concentrations (500μM) increased the activity of PLC (100%). These results suggest the possible involvement of the phosphoinositide signal transduction pathway, with the phospholipase C enzyme participating in the beneficial and toxic effects of aluminum in plants.