Abstract
One-year-old satsuma mandarin (Citrus unshiu Marc. cv. Okitsu Wase) trees on trifoliate orange rootstocks were grown in growth chambers with constant temperatures of 15, 20, 25 and 30°C and under field conditions for 6 or 8 months. The effects of temperature on root elongation, root hair development, physiological activity and free proline accumulation in the fibrous roots were investigated.
Root growth was greatly restricted at 15°C. At 30°C roots grew most vigorously, and were the longest and the heaviest. They also developed finer fibrous roots and more root hairs than at all other treatments. Length of the root hairs increased with rising temperature. The most common type of root hairs was papillate at 15°C and cylindrical in the other treatments. TTC reducing activity of the fibrous roots of trees at warm temperature (above 20°C and in the field) rapidly increased from April to June, and then decreased. However, the activity at 15°C was constant from April to June, and slightly increased from June to December. Free proline accumulated more in fibrous roots at 15°C than in other treatments. Fibrous roots of trees grown in the field accumulated much proline in December.
