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– Salinity is a major threat to agriculture. However, depending on the concentration of soluble salts in soil, increased secondary metabolite levels can occur with no major damages to plant growth and development. The phytoecdysteroid (PE) 20-hydroxyecdysone (20E) is a secondary metabolite with biotechnological, medicinal, pharmaceutical and agrochemical applicability. Here, we characterize the responses (growth and physiology) of Pfaffia glomerata under different NaCl concentrations and examine the production of 20E as affected by salinity. Forty-day-old plants grown in greenhouse were exposed to 0, 120, 240, 360 or 480 mM of NaCl for 11 days. Moderate salinity (i.e., 120 mM of NaCl) led to increased 20E concentrations in leaves (47%) relative to the control with no significant effect on photosynthesis and biomass accumulation, thus allowing improved 20E contents on a per whole-plant basis. In contrast, plants under high salinity (i.e., 240–480 mM of NaCl) displayed similar 20E concentrations in leaves compared to the control, but with marked impairments to biomass accumulation and photosynthetic performance (coupled with decreased sucrose and starch levels) in parallel to nutritional imbalance. High salinity also strongly increased salicylic acid levels, antioxidant enzyme activities, and osmoregulatory status. Regardless of stress severity, 20E production was accompanied by the upregulation of Spook and Phantom genes. Our findings suggest that P. glomerata cultivation in moderate salinity soils can be considered as a suitable agricultural option to increase 20E levels, since metabolic and structural complexity that makes its artificial synthesis very difficult.

This study examined whether drought sensitivity in acai (Euterpe oleracea Mart.) is associated with reductions in photosynthesis and increasing oxidative stress in response to down-regulation of proteins related to photosynthetic reactions, photorespiration, and antioxidant system. Well-watered (Control) and drought-stressed plants were compared when leaf water potential in stressed plants reached around − 1.5 and − 3.0 MPa, representing moderate and severe drought. Drought caused 84 and 96% decreases in net photosynthetic rate (Pn) and stomatal conductance. Stress-mediated changes in maximum quantum efficiency of photosystem II (PSII) photochemistry were unobserved, but drought decreased photochemical quenching, actual quantum yield of PSII electron transport, and apparent electron transport rate (ETR). Moderate and severe drought induced, respectively, decreases and increases in non-photochemical quenching (NPQ) and 74 and 273% increases in ETR/Pn. Moderate drought down-regulated PSII protein D2, chlorophyll a-b binding protein 8, photosystem I reaction center subunit N, sedoheptulose-1,7-bisphosphatase, and transketolase; while severe drought down-regulated LHC II proteins, ferredoxin-NADP reductase, ATP synthase subunits e and s, and carbonic anhydrase isoform X2. The glutamate–glyoxylate aminotransferase 2 and glycine dehydrogenase were down-regulated upon moderate drought, while catalase 2 and glycine cleavage system H protein 3 were up-regulated. Severe drought up-regulated glycolate oxidase, glycine cleavage system H protein 3, and aminomethyl transferase, but most of photorespiration-related proteins were only found in control plants. Down-regulation of chaperones and antioxidant enzymes and increased lipid peroxidation in stressed plants were observed upon both stress severities. Therefore, the decreases in Pn and failure in preventing oxidative damages through adjustments in NPQ and photorespiration- and antioxidant-related proteins accounted for drought sensitivity in acai.

Environmental conditions of grow can modify leaf structure and metabolite production. Neem plants produce a high amount of medicinal metabolites and contain biopesticide terpenoids with low toxicity. However, the high genetic variation and the low material quality, besides the environmental modifications warn to the need of biotechnological techniques to ensure the production of high quality metabolites. The aim was to investigate leaf structural and histochemical characteristics of Azadirachta indica grown in vitro, in vivo and acclimatized condition. It was found anatomical differences among the environments, with higher leaf thickness associated to in vivo conditions, as well as were more evenly distributed stomata. Those modifications did not qualitatively affect the production of medicinal metabolites and biopesticides. Terpenes and tannins were observed in specialized cells called idioblasts, located in the mesophyll and in the midrib region, respectively. Thus, in a qualitative approach, we can affirm that the different environments do not modify metabolites production. Increased production of these bioactive compounds could be achieved by isolation and in vitro culture of idioblasts as a new source of research in plant biotechnology.

The drought tolerance in young oil palm plants is related to greater efficiency in preventing oxidative damage by activating enzymatic and non-enzymatic antioxidant strategies simultaneously. Drought is a major environmental constraint limiting growth and yield of oil palm trees. In this study, two oil palm hybrids (BRS Manicore and BRS C 2501) were grown in large containers and subjected to a water deficit during 57 days. Leaf gas exchange analysis was combined with an in-depth assessment of the antioxidant system over the drought imposition. Under drought, leaf water potential at predawn (Ψ pd) decreased similarly in both hybrids. In parallel, there were decreases in the net CO2 assimilation rate (A), chlorophyll concentrations and Rubisco total activity. Overall, these decreases were more pronounced in BRS C 2501 than in BRS Manicore. BRS C 2501 plants triggered more markedly its enzymatic antioxidant system earlier (Ψ pd = −2.1 MPa) than did BRS Manicore, but these responses were accompanied by higher concentrations of H2O2 and malondialdehyde in BRS C 2510 than in BRS Manicore. With the progress of drought stress (Ψ pd = −2.9 MPa and below), BRS Manicore was better able to cope with oxidative stress through a more robust antioxidant system. In addition, significant decreases in drought-induced NAD+-malate dehydrogenase activities were only observed in stressed BRS C 2501 plants. Regardless of watering regimes, the total carotenoid, ascorbate and glutathione concentrations were higher in BRS Manicore than in BRS C 2501. In conclusion, BRS Manicore is better able to tolerate drought than BRS C 2501 by triggering multiple antioxidant strategies involved both in reactive oxygen species scavenging and dissipation of excess energy and/or reducing equivalents particularly under severe drought stress.

O artigo não contém resumo em português. The use of cell and plant tissues culture techniques to produce economically important active metabolites has been growing. Among these substances, azadirachtin (AZA), produced by the neem tree (Azadirachta indica), has received considerable attention due to its bioinsecticide action. The main goal of this work was to analyze the AZA levels in neem cotyledonary calli. The calli were grown in agitated Woody Plant Medium (WPM) liquid medium, supplemented with glucose (Gl), hydrolyzed casein (HC) and methyl jasmonate (MeJ) as elicitor agent. An interaction was observed between these substances, depending on in vitro cultivation time with orbital agitation. The highest concentrations (average of 0.2470 µg g-1) of AZA were produced in the first and second weeks of culture when the cell mass was grown in a medium with 2% Gl v/v, 500 mg L-1 HC and 100 µM of MeJ. This corresponded to approximately 57% of the AZA content stored in the donor plants seeds, used as a source of explants to induce in vitro callus formation. It was concluded that the nutrition, as well as the concentration of MeJ as signal transduction of secondary metabolism in neem cells, might influence the AZA content produced in vitro.

The hypothesis that application of exogenous glycine betaine (GBEX) may attenuate the effects of mild water deficit in leaf gas exchange and lipid peroxidation in Carapa guianensis was examined. For this reason, 110-d old plants were sprayed with 0, 25, and 50 mM GBEX and then subjected to two watering regimes. In the first, irrigation was continuously performed to maintain the soil near to field capacity (watered plants). In the second, irrigation was withheld and water deficit resulted from progressive evapotranspiration (water-stressed plants). Treatment comparisons were assessed when predawn leaflet water potential (Ψpd) of stressed plants reached −1.28 ± 0.34 MPa. Regardless of the watering regime, significant (P

Two acai plant materials (BRS-PA cultivar and Hideo ecotype) were subjected to differential irrigation to examine its potential tolerance to water deficit. Seedlings were grown for 45 days under irrigation replacing different volumes of water required to the soil reaches field capacity (FC). The irrigations replaced 100% FC (control treatment), 70% FC, and 40% FC (water deficit treatments). The Hideo ecotype showed more significant decreases in leaf water potential than BRS-PA. The former showed lower net CO2 assimilation rate (A), stomatal conductance (g s), transpiration and instantaneous water use efficiency, particularly under irrigation of 70% FC. In Hideo, the decreases in A mediated by water deficit were coupled to chlorophyll (Chl) degradation. In BRS-PA, the A and Chl content were decreased only under 40% FC. Starch content was unchanged between plant materials irrigated with 70% FC; however, it was decreased in Hideo seedlings irrigated with 40% FC. Accumulation of total soluble carbohydrates, glucose, and fructose has occurred in Hideo ecotype under 70% FC and in both plant materials under 40% FC. The water deficit caused more striking decreases in Hideo growth than in BRS-PA, especially by reducing leaf dry matter, root dray matter (under 70% FC), and both total and specific leaflet areas. Under irrigation with 40% FC, plant material differences in growth variables were negligible. The results indicate that BRS-PA cultivar tolerate mild water deficit (70% FC) more satisfactorily than Hideo; however, both plant materials were equally sensitive to more severe water deficit (40% FC).

Young Carapa guianensis plants were examined under well-watered (control) and water-deficit conditions with the aim to evaluate possible relationship between diurnal changes in leaflet gas exchange with lipid peroxidation and adjustments in antioxidative responses. Treatment comparisons were assessed when leaflet water potential (Ψw) in water-stressed plants reached around −2.5 ± 0.5 MPa at pre-dawn. Regardless of watering regime, the highest net CO2 assimilation rate and stomatal conductance were recorded until 9:00 h. Control plants showed diurnal increases in transpiration, while it was strongly decreased in water-stressed plants. Diurnal decreases in intercellular to ambient CO2 concentration ratio were just observed in stressed plants. Regardless of watering regime, non-significant changes (P > 0.05) in Ψw and relative water content were registered throughout the day; however, both variables were significantly lower (P

Changes in chloroplastidic pigments, gas exchange and carbohydrate concentrations were assessed during the rapid initial expansion of C. guianensis leaflet. Leaves at metaphyll stage were tagged and assessments were carried out 14, 17, 20, 23, 27, and 31 days later. Pigments synthesis, distribution and accumulation were uniform among leaflet sections (basal, median and apical). Chlorophyll (Chl) a, Chl b, Chl (a+b), and total carotenoids (Car) concentrations were significantly increased after 27 days from metaphyll, and the most expressive increases were parallel to lower specific leaflet area. Chl a/b was lower on day 14 and it was increased on subsequent days. Negative net photosynthesis rate (P N), and the lowest stomatal conductance (g s) and transpiration (E) were registered on day 14, following significant increases on subsequent days. The Chl (a+b) and Chl a effects on P N were more expressive until day 20. Intercellular to ambient CO2 concentration ratio (C i/C a) was higher on day 14 and lower on subsequent days, and no stomatal limitation to CO2 influx inside leaflets was observed. Leaflet temperature was almost constant (ca. 35°C) during leaflet development. Sucrose and starch concentrations were increased in parallel to increases in P N. Altogether, these results highlight the main physiological changes during C. guianensis leaflet expansion and they should be considered in future experiments focusing on factors affecting P N in this species.

In vitro propagation of neem (Azadirachta indica A. Juss.) may offer an efficient alternative to seed propagation of this species. For optimization of in vitro propagation, different basal salt formulations, growth regulators, and culture container sealants (polytetrafluoroethylene hydrophobic membranes [PTFE]) were evaluated. Nodal segments cultured on Murashige and Skoog (MS) medium showed the highest shoot formation per explant (1.67). Explants cultured in flasks containing MS medium with 0.5 mg L−1 benzyladenine, 0.5 mg L−1 kinetin, and 0.05 mg L−1 naphthaleneacetic acid, and sealed with two PTFE membranes, produced the highest number of shoots (4.04). In contrast, explants cultured in flasks without membranes showed leaf chlorosis and senescence. For plant recovery, regenerants were acclimatized in a substrate of coconut fiber and eucalyptus bark (1:1) and showed 80% survival. Our results indicated that the use of flasks with vents was beneficial for in vitro propagation of this important plant.

The ecdysteroid 20-hydroxyecdysone (20E) is a steroid hormone found in insects and few plants. To analyze its temporal and spatial distribution in Pfaffia glomerata (Amaranthaceae), we selected among 71 accessions, the accession 13 which showed the highest root 20E total quantity (1.48 g/plant root). The 20E was constantly detected in flowers, leaves, stems, and roots, but its percentage was variable throughout its development. The highest 20E percentage was found in flowers (0.82%), roots (0.66%), leaves (0.60%), and stems (0.24%). While stems showed the least variable 20E percentage (0.13% - 0.24%), followed by roots (0.42% - 0.66%), and flowers (0.47% - 0.82%). Leaves showed the greatest 20E percentage variation (0.21% - 0.60%). The stem and leaves 20E total amount remained constant, showing a little variation while root 20E total amount increased over time, suggesting that 20E may be accumulated in roots. These findings suggest that 20E has tissue specific functions in plant and may have ecological significance since uncoordinated pulses of 20E are often lethal to insects.

Annually, plants produce about 180 billion tons of cellulose making it the largest reservoir of organic carbon on Earth. Cellulose is a linear homopolymer of beta(1-4)-linked glucose residues. The coordinated synthesis of glucose chains is orchestrated by specific plasma membrane-bound cellulose synthase complexes (CelS). The CelS is postulated to be composed of approximately 36 cellulose synthase (CESA) subunits. The CelS synthesizes 36 glucose chains in close proximity before they are further organized into microfibrils that are further associated with other cell wall polymers. The 36 glucose chains in a microfibril are stabilized by intra- and inter-hydrogen bonding which confer great stability on microfibrils. Several elementary microfibrils come together to form macrofibrils. Many CESA isoforms appear to be involved in the cellulose biosynthetic process and at least three types of CESA isoforms appear to be necessary for the functional organization of CelS in higher plants.