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The different growth responses under salinity in relation to the carbon partitioning and sucrose metabolism in both sink and source organs have been studied in a salt‐tolerant (cv. Pera) and in a salt‐sensitive (cv. Volgogradskij) tomato genotype (Lycopersicon esculentum Mill.). After 3 weeks of salinization, the plant dry weight was reduced by 12–34% in cv. Pera and by 45–58% in cv. Volgogradskij. Photosynthesis was positively correlated to plant growth in cv. Pera but not in cv. Volgogradskij. In this salt‐sensitive genotype, both photosynthesis and growth were negatively correlated with fructose, glucose and sucrose accumulation in both mature and young leaves, suggesting a blockage in their use for growth. The transient accumulation of sucrose and hexoses in the young leaves of cv. Pera was linked to increases in all soluble sucrolytic activities, mainly acid invertase (EC 3.2.1.25) and sucrose synthase (EC 2.4.1.13), which was related to sink activity and growth capacity. The sucrose‐phosphate synthase activity (EC 2.4.1.14) was related to the ability of mature leaves to regulate assimilate production, accumulation and export. The salt‐tolerant cv. Pera accumulated a higher amount of total carbohydrates, but cv. Volgogradskij showed the highest soluble fraction under salinity. The carbohydrate availability and the photosynthetic rate do not seem to be the first limiting factors for plant growth under saline conditions, but the different behavior observed in both genotypes concerning the distribution and use of photoassimilates could help to explain their different salt‐tolerance degrees.

Mycorrhizal and non-mycorrhizal tomato plants (Lycopersicon esculentum Mill. cv ‘Amalia’) were subjected to water stress by withholding irrigation water for 72 hours and then reirrigated for 120 hours. Water stress reduced root mycorrhizal colonization, although the presence of the fungus Glomus clarum stimulated tomato plant growth. During the stress period the effect on the growth was more pronounced in aerial biomass than in the root biomass. The decrease in the soil water potential generated a decrease in leaf water potential (Ψl) and leaf turgor potential (Ψt), particularly in the non-mycorrhizal plants. Although the absence of osmotic adjustment provoked the loss of turgor in stressed plants, both Ψl and Ψt recovered after a short reirrigation period. Mycorrhizal infection improved photosynthetic activity (Pn) and stomatal conductance (gs) in non-stressed and stressed plants. These increases were accompanied by higher root hydraulic conductivity values, indicating enhanced water uptake in drought conditions. Neither Pn nor gs fully recovered after rewatering. The beneficial effect of the mycorrhizal symbiosis on the water status of tomato plants stimulated plant growth.