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This study examines the effect of the exogenous application of polyamine putrescine together with the application of different ratios of nitrate/ammonium (NO3−/NH4+), on the physiology of cauliflower subjected to heat stress. The 50:50 NO3−/NH4+ ratio was the best ratio against heat stress. As a result of the joint application of these compounds, a higher photosynthetic rate, a higher accumulation of both photosynthesis-related compounds and pigments, total proteins, and a change in the status of nutrients were obtained. Particularly, the decrease in content of calcium, chloride and sulphate in plants under heat stress is ameliorated by the ammonium effect. Additionally, it is important to highlight that cauliflower waste contains a higher content of mineral nutrients than floret cauliflower. These effects were more marked in young leaves. Furthermore, a synergistic effect for coping with heat stress between the polyamine and the nutritional treatment was observed. For this, both the application of putrescine and the feeding of plants with a 50:50 NO3−/NH4+ ratio before heat stress is proposed for the first time as an agricultural practice for increasing the thermotolerance of cauliflower cv Moonshine. On the other hand, due to the lower lipid peroxidation rate obtained in cauliflower leaves, these plants could be used for health purposes as ointments or other nutraceutical products, making the cultivation of this kind of cruciferous more sustainable.

We investigated the effect of supplying nitrogen, as NO or as NO/NH, on the composition of fruits of sweet pepper (Capsicum annuum L. cv. Melchor) plants grown with different CO concentrations ([CO]): ambient or elevated (800 μmol mol). The results show that the application of NH and high [CO] affected the chroma related to the concentrations of chlorophylls. The concentrations of Ca, Cu, Mg, P, and Zn were significantly reduced in the fruits of plants nourished with NH, the loss of Fe being more dramatic at increased [CO], which was also the case with the protein concentration. The concentration of total phenolics was increased by NH, being unaffected by [CO]. Globally, the NH was the main factor that affected fruit free amino acid concentrations. Polyamines were affected differently: putrescine was increased by elevated [CO], while the response of cadaverine depended on the form of N supplied.

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