Garden post-transplant effects of pre-transplant plug cell volume and growing medium quality (as abiotic stresses) in Impatiens walleriana

Although much is known about the production of bedding plants, including Impatiens walleriana, little has been documented on their post-production performance. Thus, the aim of this work was to understand how pre-transplant crop management related to root restrictions imposed by plug cell volume and substrate quality affects the post-production performance related to biomass accumulation. To this end, we tested four plug cell volumes, as well as four growing media with significantly different physical and chemical properties, during nursery and pot culture. We also evaluated the difference between use and nonuse of synthetic cytokinin spray (benzyl aminopurine, BAP), a proven stress alleviator. Our novelty data validated the previous hypothesis and showed that plant quality and garden performance are dependent on these potential stress sources. The physiological mechanisms involved included differences in leaf area expansion (estimated mainly by relative leaf area expansion rate) and differences in CO2 fixation capacity (estimated by net assimilation rate). The sum of these responses determined significant differences in total fresh and dry weight during pot culture, which were amplified when plants were transplanted to a field bed. Spraying plants with synthetic cytokinin early during nursery allowed overriding of most root restriction abiotic stresses related to plug cell volume and growing media; therefore, synthetic cytokinin constitutes a tool to improve the yield of bedding plants (at the grower's level) and garden performance.

Molecular weight and concentration of chitosan affect plant development and phenolic substance pattern in arugula

The present research reports the role of chitosan’s molecular weight (1, 10, and 100 kDa) on the differentiation of its effects on arugula (Eruca vesicaria ssp. sativa) cultivation in a controlled environment. The leaves' phenolic substance pattern from the plants treated with the chitosan variant that gave the best developmental results was analyzed through a reversed-phase HPLC. The leaf production was enhanced after 10 kDa chitosan treatment at 5 mg L-1, while the leaf area expansion was significantly improved after 1 and 100 kDa chitosan at 20 mg L-1 and 10 kDa chitosan at 5 mg L-1. The plant's rhizogenic development was restricted after all chitosan treatments regardless of their molecular weight and concentration. The contents of chlorophyll b and carotenoids increased after the treatments; however, chlorophyll a content was not significantly affected by the treatments and remained unchanged. The chromatographic analysis showed that 10 kDa chitosan treatment at 5 mg L-1 increased gallic acid, rutin, and p-coumaric acid contents and made significant changes in the individual phenolic substance pattern. The current study indicated that direct application of chitosan to soil restricts root production in arugula but enhances foliar growth, which is beneficial to producers. On the other hand, constant- or over-treatment with chitosan could inhibit root growth and further lead to developmental deficiencies sourced by nutrient uptake disorders. The use of chitosan as an organic and natural biostimulant in controlled-environment agriculture could be a better option than synthetic growth stimulants.

Responses of Rice Growth to Day and Night Temperature and Relative Air Humidity—Leaf Elongation and Assimilation

Predictions of future crop growth and yield under a changing climate require a precise knowledge of plant responses to their environment. Since leaf growth increases the photosynthesizing area of the plant, it occupies a central position during the vegetative phase. Rice is cultivated in diverse ecological zones largely differing in temperature and relative air humidity (RH). To investigate the effects of temperature and RH during day and night on leaf growth, one variety (IR64) was grown in a growth chamber using 9 day/night regimes around the same mean temperature and RH, which were combinations of 3 temperature treatments (30/20 °C, 25/25 °C, 20/30 °C day/night temperature) and 3 RH treatments (40/90%, 65/65%, 90/40% day/night RH). Day/night leaf elongation rates (LER) were measured and compared to leaf gas exchange measurements and leaf area expansion on the plant level. While daytime LER was mainly temperature-dependent, nighttime LER was equally affected by temperature and RH and closely correlated with leaf area expansion at the plant level. We hypothesize that the same parameters increasing LER during the night also enhance leaf area expansion via shifts in partitioning to larger and thinner leaves. Further, base temperatures estimated from LERs varied with RH, emphasizing the need to take RH into consideration when modeling crop growth in response to temperature.

Interactions between plant hormones and light quality signaling in regulating the shoot growth of Arabidopsis thaliana seedlings

The effects of a decrease in red to far-red (R/FR) ratio on shoot growth of two-week-old Arabidopsis thaliana (L.) Heynh. seedlings were examined in the context of possible causal involvement of key plant growth hormones. Decreasing the R/FR ratio significantly increased petiole elongation and leaf area expansion of the Columbia (Col) line seedlings. In contrast, seedlings of the Landsberg erecta (Ler) line showed no significant change in leaf area and only a marginal increase in petiole growth. This low R/FR ratio-induced growth was accompanied by significant increases in concentrations of the growth “effector” gibberellin (GA4) and an auxin (indole-3-acetic acid (IAA)) in shoot tissues of Col. However, cytokinins (CKs) in Col shoot tissues were decreased and ethylene evolution was reduced when the R/FR ratio was decreased from that of normal sunlight to a low R/FR ratio. Several A. thaliana genotypes with plant hormone-related mutations were also assessed, including auxin resistant, axr2-1; GA insensitive, gai-1; and ethylene over-producing, eto2. None of these increased their petiole length or leaf area growth in response to lowering the R/FR ratio. We thus conclude that both GA4 and IAA are causally involved in the increased shoot growth of A. thaliana Col seedlings that occurs in response to a lower than normal R/FR ratio.

Morphological indicators and the time of transition to flower in Ptilotus nobilis (Amaranthaceae)

Floral initiation of Ptilotus nobilis (Lindl.) F.Muell. was investigated by both scanning electron and light microscopy to develop a template for the transition from vegetative to reproductive growth. Four developmental stages were identified, including two vegetative and two reproductive stages. Bract initiation was accompanied by a significant increase in meristem area and diameter, and was defined as the onset of flowering. At the transition, meristem diameters and areas increased 1.5 and 2.3 times, respectively. Most morphological traits, including leaf number, mean leaf area and total leaf area, increased gradually at the time of transition and were further investigated in a subsequent glasshouse trial. Floral initiation occurred very early and at 25 days after sowing all plants had entered the reproductive phase. At the onset of flowering leaf and node number increased significantly with 3.6 and 4.2, respectively. Branching and leaf area expansion were identified as post-initiation processes, and increased by 2.8 (total foliage area), 3.3 (total leaf area) and 1.8 (mean leaf area). During the vegetative phase a discolouration of the shoot apical meristem was noted and underlying reasons are discussed.