In ornamental plants growing in pots, root restriction would be presumably related to an endogenous long-distance cytokinin signal from roots. In this context, it has been recently indicated that, in potted ornamental plants, a single 6-benzylaminopurine (BAP) spray can be used to increase biomass accumulation. Although cytokinin sprays and cytokinin-containing substances have been previously used to improve growth in cacti, the physiological mechanism involved has not been elucidated. Thus, this work aimed to evaluate the effect of a single BAP spray on the growth of the vegetative axillary stems of the cactus Mammillaria elongata subsp. echinaria. To achieve this general objective, M. elongata subsp. echinaria plants were sprayed with 0, 5, 50, 100 or 200 mg L-1 BAP solutions (40 plants per treatment) and grown for 210 days under greenhouse conditions. The results showed that a single BAP spray increased both fresh and dry weights, photosynthetic stem area, root length and a number of axillary stems at 90 days after the beginning of the experiment. The higher biomass accumulation was related to a higher rate of stem area expansion (RSAE), relative growth rate (RGR), net assimilation rate (NAR) and partitioning of photoassimilates into stems. This results indicate that M. elongata subsp. echinaria biomass accumulation can be increased by a single BAP spray of 5 mg L-1, although the highest response was found with a 200 mg L-1 BAP spray.
Plants raised in small cell trays are often subjected to root growth restrictions. Root tips are a source of cytokinin, and insufficient biosynthesis and transport of this hormone to the aerial part severely impairs shoot development. Exogenous supply of cytokinin to the foliage has been shown to effectively counteract these effects in several horticultural crops, but the physiological processes involved are still unclear. The aim of this work was to study the effect of spraying the cytokinin 6-benzylaminopurine (BAP) on growth and development of plug lettuce seedlings focusing on the morpho-physiological mechanisms involved in plant response. Two experiments were conducted in a greenhouse. Lettuce (Lactuca sativa L. Crimor INTA) seedlings were grown for 35 days in 128-, 200- and 288-cells trays (17.37, 13.90 and6.18 cm3 ·cell-1 respectively), after which they were sprayed with BAP (6-benzylaminopurine) solutions (0, 5, 50 or 100 mg·L-1) either immediately before transplant, or 7 days after transplant. Seedlings were transplanted into larger (3,000 cm3) pots in which they grew for further 60 days. Decreasing plug cell volume resulted in a steep decrease in plant net assimilation rate and leaf net photosynthetic rate, but the impact on the relative growth rate was somewhat lower due to an increased leaf area ratio. BAP sprays increased plant biomass accumulation and enhanced the development of photosynthetic area, in parallel with a strong promotion of carbon assimilation, and these effects were more remarkable in plants raised in smaller plugs, and when hormone was supplied at the pre-transplant stage.
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