Effects of Different Nitrogen Forms and Exogenous Application of Putrescine on Heat Stress of Cauliflower: Photosynthetic Gas Exchange, Mineral Concentration and Lipid Peroxidation

Abstract

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.

The Effect of Foliar Putrescine Application, Ammonium Exposure, and Heat Stress on Antioxidant Compounds in Cauliflower Waste

“…Several studies carried out in some plants of Brassicaceae family noticed that if the exposure temperature of these plants exceeds their physiological threshold (32 • C), it can lead to an increase in reactive oxygen species (ROS) within its cells, and oxidative stress may be developed when ROS exceed antioxidant defenses [3,4]. Furthermore, it is important to to that non-edible part of cauliflower with nutraceutical purposes [15,21]. In addition, putrescine is the precursor of other polyamines with a higher molecular weight or more nitrogen atoms in their structure, such as spermidine and spermine [21][22][23][24][25].…”

“…Furthermore, it is important to to that non-edible part of cauliflower with nutraceutical purposes [15,21]. In addition, putrescine is the precursor of other polyamines with a higher molecular weight or more nitrogen atoms in their structure, such as spermidine and spermine [21][22][23][24][25].…”

“…In fact, several studies [ 5 , 20 ] reported that higher levels of free and bound polyamines in plants were obtained as consequence of the exposure of plants to heat stress. Moreover, recent studies have suggested that polyamines can be used in order to enhance the tolerance to heat stress, allowing to obtain a higher total production yield and higher quality of the final plant products [ 19 , 21 ]. In nature, polyamines are often found as free molecules, but they can also be found in conjugated or bound forms.…”

“…This takes place not only in inflorescence, but also in leaves of different plants. This can lead to both cauliflower more attractive by consumers and by-products cauliflower with add-value, which can allow give an additional valorization to that non-edible part of cauliflower with nutraceutical purposes [ 15 , 21 ]. In addition, putrescine is the precursor of other polyamines with a higher molecular weight or more nitrogen atoms in their structure, such as spermidine and spermine [ 21 , 22 , 23 , 24 , 25 ].…”

“…Thus, a possible solution in order to improve both the plant quality and obtaining an improved number of bioactive compounds can be vary the nutritional solution. Regarding the response of that modulation on the heat stress, some previous studies have shown that the application of NO 3 − /NH 4 + in adequate proportions can alleviate oxidative stress caused by heat stress [ 21 , 27 ]. Moreover, Munene in a study carried out with amaranth species [ 28 ] indicated that a high exposure of plants to NH 4 + can be reflected in a higher accumulation of all polyamines, including putrescine, cadaverine, spermidine, and spermine.…”