Search

Previous research demonstrated that the interval between defoliation treatments based on the leaf stage is a promising tool for the management of annual ryegrass (Lolium multiflorum L.) pasture. The use of this tool, which is based on the physiological status of the plant, could also benefit the seed production. We assessed the effects of the time of defoliation based on leaf stage on seed yield and quality of annual ryegrass cut to three residual stubble heights (RSH) (50%, 25% and 0% of plant height pre-defoliation) and a second defoliation applied to certain treatments based on the leaf stage of the plant regrowth (two or three leaves per tiller). Higher defoliation intensities (lower RSH) increased the amount of harvested forage to 4.0 t DM ha–1. Moderate defoliation (50%) undertaken at the 3-leaf stage combined with intense defoliation (25% and 0%) at the 2-leaf stage resulted in the highest seed yields (1.8 t ha–1). However, lower RSH reduced mean seed weight and physiological seed quality, which was also associated with lower seed starch and protein content. Accelerated ageing (AA) tests were used to compare seed vigour between treatments. A second defoliation at the 3-leaf stage plus intense defoliation (RSH 0%) resulted in seed lots with a high rate of lipid peroxidation after the AA test, followed by lower catalase activity, germination, and seedling growth. The combination of a second defoliation at the 3-leaf stage and the retention of higher RSH (50%) promoted a greater proportion of leaf blades in the stubble, with a strong positive correlation with seed production and vigour. Antioxidant enzyme activity after the AA test is an important marker of annual ryegrass seed quality.

This study aimed to assess the capacity of two methods of application of salicylic acid (SA) to mitigate the effects of water deficit during the vegetative growth of tomato (Solanum lycopersicum L.) plants comparatively evaluated by growth, physiological and biochemical responses. Under greenhouse conditions, a combination of two factors was tested. The first was SA application: without SA, seed priming with SA, and soil drench with SA solution at 19 days after seedling emergence. The second factor, water limitation (20, 30, 40, and 100% of water holding capacity of the substrate) was applied 28 days after seedling emergence for 5 days. Results showed that plant growth and photosynthetic activity were significantly inhibited by the water deficit. On the other hand, water use efficiency, activities of superoxide dismutase, ascorbate peroxidase, catalase and contents of malondialdehyde, hydrogen peroxide and osmoprotectants were significantly increased by water deficit. Seed priming with SA induced increases in leaf area, root dry weight and root/shoot ratio under drought conditions. Soil drench with SA induced improvements in CO2 assimilation rate and stomatal conductance in well-irrigated plants. Even when, in general, the activity of antioxidant enzymes was not increased by the application of SA, the cellular redox homeostasis was maintained through increases in the contents of proline and total soluble sugars from the degradation of starch. Seed priming with SA is a suitable technique to mitigate the damaging effects of severe water deficit while maintaining plant growth.

This study aimed to investigate the leaf anatomy of Jacquinia armillaris plants in two different Venezuelan xeric shrublands to evaluate possible variations caused by the environments, which differ in rainfall and soil salinity. Leaf samples were collected in two sites: La Tortuga Island, a dryer and salty environment than the other collecting site, Turpialito, a coastal location in the mainland. The epidermis and the mesophylls were observed with a light microscope and measured with an ocular micrometer inserted in one of the eyepieces. The results show that J. armillaris has many characteristic anatomical traits of xerophytes, among them: thick cuticles and thick epidermis in both leaf surfaces, stomata only in the abaxial side and epidermal depressions lodging a glandular trichome. Leaves are bifacial and present multistratified palisade parenchyma facing the adaxial epidermis and abaxial spongy parenchyma with abundant intercellular spaces. Furthermore, the hypodermis is composed of one or two cell layers below the upper epidermis. Leaf lamina dimension, petiole, cuticles, epidermis and hypodermis cells, as well as the stomatal occlusive cells and number of trichomes, had differences in size and number when the plants of both sites were compared, being higher in plants from La Tortuga. On the other hand, palisade parenchyma and stomatal density were higher in Turpialito plants. Plants collected in La Tortuga Island showed characteristics that suggest adaptation to the island’s saline and more arid conditions in comparison to plants from Turpialito, which presented more leaf traits related to adaptations to water deficit. These results demonstrate the phenotypic plasticity of J. armillaris plants that grow in two different xeric shrublands.

It is time to recognize the existence of plant memory, a phenomenon that allows plants to store and recall information from previous events and then change their responses to future stressful conditions. Although many recent publications have addressed this topic and concluded about plant memory using either classical or advanced approaches, several scientists are still armored against this important concept inherent to life and found in plants. Herein, our aims are to clarify the concept of memory and its use in plants and to overview the mechanisms underlying plant memory. How do plants store information? Where is such information stored? How long can information be stored? How does memory affect the organization of a given system with such ability? These are some questions that deserve attention from the scientific community rather than inadequate and incoherent ones challenging the existence of plant memory. Let us move on to the next page and deal with plants as living beings.

Germinação de sementes e atividade de enzimas antioxidantes em plântulas de grama forquilha diplóide e tetraploide sob restrição hídrica RESUMO: O presente estudo objetivou avaliar as respostas fisiológicas de dois genótipos de grama forquilha (Paspalum notatum Flügge) sob restrição hídrica induzida por polietileno glicol (PEG6000) durante a germinação de sementes. Sementes da cv. Pensacola (diplóide) e do ecótipo Bagual (tetraplóide) foram colocadas em papel umedecido com soluções osmóticas nos potenciais de 0,0; -0,1; -0,2 e -0,3 MPa. Composto de duas subamostras de 100 sementes e quatro unidades experimentais por tratamento, o teste de germinação foi conduzido em câmara de germinação sob temperatura alternada de 30-20 ºC, com presença de luz durante a maior temperatura. Foram avaliados a porcentagem final e o índice de velocidade de germinação das sementes, assim como o crescimento inicial, a atividade e a expressão de enzimas antioxidantes das plântulas. A restrição hídrica induzida por PEG6000 reduziu o percentual de germinação em Pensacola (de 74 para 59%) e Bagual (34 para 10%). Este último, na avaliação de plântulas, apresentou massa seca superior em relação à cv. Pensacola (1.7 vezes superior em raiz e 1.6 vezes superior em parte aérea). Em resposta à restrição hídrica moderada, os genótipos apresentaram aumentos tanto do crescimento radicular (1.7 vezes superior em -0.1 em comparação com 0.0 MPa), quanto da expressão e da atividade enzimática (superóxido dismutase e catalase). Palavras-chave: Paspalum notatum Flügge, ecótipo, polietilenoglicol, estresse por seca, estresse oxidativo. Made available in DSpace on 2020-12-08T09:06:44Z (GMT). No. of bitstreams: 1 kopp-2020.pdf: 1220946 bytes, checksum: 3976727ce52ae98c47d48ea86409b490 (MD5) Previous issue date: 2020