The Never ripe Mutant Provides Evidence That Tumor-Induced Ethylene Controls the Morphogenesis of Agrobacterium tumefaciens-Induced Crown Galls on Tomato Stems

We confirm the hypothesis that Agrobacterium tumefaciens-induced galls produce ethylene that controls vessel differentiation in the host stem of tomato (Lycopersicon esculentum Mill.). Using an ethylene-insensitive mutant, Never ripe (Nr), and its isogenic wild-type parent we show that infection by A. tumefaciens results in high rates of ethylene evolution from the developing crown galls. Ethylene evolution from isolated internodes carrying galls was up to 50-fold greater than from isolated internodes of control plants when measured 21 and 28 d after infection. Tumor-induced ethylene substantially decreased vessel diameter in the host tissues beside the tumor in wild-type stems but had a very limited effect in the Nr stems. Ethylene promoted the typical unorganized callus shape of the gall, which maximized the tumor surface in wild-type stems, whereas the galls on the Nr stems had a smooth surface. The combination of decreased vessel diameter in the host and increased tumor surface ensured water-supply priority to the growing gall over the host shoot. These results indicate that in addition to the well-defined roles of auxin and cytokinin, there is a critical role for ethylene in determining crown-gall morphogenesis.     

Plasticity and variability in the patterns of phytolith formation in Asteraceae species along a large rainfall gradient in Israel

Silicification and phytolith formation in Poaceae species growing in arid and semi-arid regions are commonly thought to be positively correlated with silica and water availabilities and with transpiration. To expand our understanding of this phenomenon, we chose to study species of the Asteraceae, the largest dicotyledonous family. We measured phytolith concentrations in eight Asteraceae species (three non-spiny and five spiny) and one Poaceae species (Avena sterilis), as reference, along a large climatic gradient of 80–900 mm mean annual rainfall in Israel.