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This study aimed to evaluate the effect of putrescine priming on the initial growth, chlorophyll fluorescence, primary metabolites accumulation, and antioxidant enzyme activities in two maize hybrids with contrasting drought tolerances. Seeds of Zea mays L. hybrids DKB 390 (drought tolerant) and BRS 1030 (drought sensitive) were primed with putrescine (10 or 100 µM). Paper rolls moistened with distilled water or mannitol (-0.6 MPa) were maintened at 30°C for 7 d. The growth parameters were higher in the DKB hybrid than in the BRS hybrid. Putrescine priming (10 µM) promoted the root growth of BRS at levels similar to those of DKB and improved photochemical and non-photochemical quenching and maximum quantum efficiency of BRS seedlings. Higher levels of reducing sugars were found in DKB seedlings when compared to BRS in both roots and leaves, especially with 100 µM putrescine. Total soluble sugar and starch were lower in the maize roots under water deficit and with 10 µM putrescine for both hybrids. BRS seedlings showed higher starch content in the leaves in the control and 10 µM putrescine treatments. Superoxide dismutase was activated in BRS plants by the priming, especially in the roots, but this effect was not observed for catalase, ascorbate, or guaiacol peroxidase, although the DKB seedlings presented much higher guaiacol peroxidade activity than BRS seedlings in both the roots and shoots. In conclusion, putrescine priming (10 M) improved the morphological and biochemical responses of the drought sensitive maize hybrid BRS.

Studies that simulate recurrent drought events with subsequent episodes of rehydration better reflect natural conditions and allow visualization of differential acclimatization responses resulting from memory and tolerance mechanisms. Piper aduncum and Piper tuberculatum were grown in a greenhouse and were subjected to three successive cycles of drought and subsequent rehydration. After suspending irrigation, gas exchanges were measured daily with IRGA. When stomatal conductances close to zero were obtained, the plants were rehydrated and kept irrigated. In P. tuberculatum, stomatal conductance was always higher after periods of rehydration compared to the period before the drought, while the transpiration rate was lower only during the drought. The damage to the photosynthetic apparatus was caused by the influence of the interception of the flow of electrons in the transport chain. We came to the conclusion that the dehydrated plants showed an alert signal, which triggered response mechanisms to prevent or deal with the water stress situation.

This study investigates how cocoa rootstocks respond to flooding and post-flooding conditions, offering insights for cocoa plantation sustainability in flood-prone areas due to climate change. We studied Theobroma cacao L. rootstocks for 60 d of flooding and 30 d post-flooding, grafting PS-1319 scions onto five rootstocks (TSH-1188, Cepec-2002, Pará, Esfip-02, SJ-02). Photochemical performance remained stable across rootstocks, while flooding progressively reduced electron transport efficiency. Photochemical damage emerged after 7 d, worsening occurred at 19 d. Although post-flooding efficiency improved, recovery time was insufficient for full restoration. Stem diameter increased less in Esfip-02. TSH-1188 had the highest stem dry mass during flooding and the most root and total dry mass during post-flooding. SJ-02 had the lowest stem dry mass and post-flooding total dry mass. Principal component analysis revealed stem and root development as a key for recovery. SJ-02 and Esfip-02 showed lower flooding tolerance and recovery, while TSH-1188 and Pará exhibited higher resilience.

In Brazil savanna type of soils presents problems with phosphorus content. The selection and identification of maize genotypes to such environments is a high priority of Brazilian research. The purpose of this paper was to evaluate, in soils with different P concentrations, the dry mass attributes and characteristics of root morphology in eight maize lines with different genetic background and origins of the Breeding Program of the National Research Center for Maize and Sorghum. The experiment was carried out in plots prepared with two levels of phosphorus: high phosphorus (HP) and low phosphorus (LP). The experimental design was randomized blocks with three replications. The evaluation of the characteristics of the shoots and the root system morphology was performed 21 days after sowing. The WinRhizo program of images analysis was used for the root morphology. There were no differences between the phosphorus levels for the dry mass attributes. However, when we compared P levels, root morphology of L13.1.2 strain performed the highest surface area (SA) and total root length (RL), length of thin (TRL) and very thin (VTRL) roots in low P concentration. The root systems digital images analysis techniques allowed efficient discrimination of maize genotypes in environments with low P levels.

Changes in root anatomical structures at successive cycles of selection (cycle 1 to cycle 18, alternating) were observed in the study of maize (Zea mays L. cv. Saracura-BRS 4154) capable to survive and produce in temporarily flooded soils; this cultivars was developed by the Maize and Sorghum National Research Center through stratified phenotypic recurrent selection for cultivation wetland soils. Field trial was carried out and flooding of the soil was initiated at the six-leaf stage; the soil was flooded with water (20-cm deep) three times per week. Root sample was collected, fixed, and selected for observation in photon microscope. A gradual increase in the number of aerenchyma, the proportion of vascular cylinder, smaller metaxylem, and phloem and epidermis width, and a decrease in exodermis and cortex were observed in successive selection cycles. Such phenotypic changes impart the flood tolerance ability to this maize cultivar.