PROBLEM TO BE SOLVED: To provide a plant, such as tomato, having increased plant vigor and the plant is further endowed with heat tolerance.SOLUTION: A mutant Della protein is retained in which a leucine corresponding to leucine at position 567 in the amino acid sequence of the Della protein is replaced with another amino acid, preferably with phenylalanine, whereby a cucurbitaceous or solanaceous plant, especially a plant such as tomato, is obtained which has not only increased plant height, but a thick stem and heat resistance.【課題】草勢が強化され、さらに耐暑性が付与されたトマトなどの植物を提供する。【解決手段】Dellaタンパク質のアミノ酸配列において、567位のロイシンに相当するロイシンが他のアミノ酸、好ましくはフェニルアラニンに置換された変異型Dellaタンパク質を保有することで、草丈が高くなるだけでなく、茎が太くなり、耐暑性を有したウリ科又はナス科の植物で、特にトマト等の植物。【選択図】図１
