Uptake and metabolism of 6-benzylaminopurine in shoot cultures of

Shoots of Gerbera jamesonii Bolus, cultured in vitro were induced to multiply by the addition of 2.22 μ M 6-benzylaminopurine (BAP) to the medium. Shoots growing in the presence of [¹⁴C]-BAP were harvested every 4 days and sub-divided into petioles plus apices, laminae and basal callus. The 3- and 9-glucosides, 9-riboside and a novel compound, the 9-ribosylglucoside were characterised as metabolites of BAP by mass spectrometry. The 9-riboside was the principal metabolite formed initially in petioles plus apicies and callus but further metabolism varied depending on tissue type. After 24 days the major metabolite in the callus was the 9-ribosylglucoside, with only trace amounts of the other metabolites present. In contrast, both 3-glucoside and 9-ribosylglucoside accumulated in petioles plus apices whereas the 3-glucoside accumulated in laminae.     

Whitefly control in cut gerbera: is it possible to control Trialeurodes vaporariorum with Encarsia formosa?

We investigated the impact of inundative releases of the parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae), for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood), on cut gerbera (Gerbera jamesonii L.) under controlled greenhouse conditions. Experimental units consisted of ten plants covered and separated from other units by gauze tents. We assessed three release rates of the aphelinid parasitoid: a 7-week experiment with a standard release rate (10 m⁻²/14 days), and a subsequent 3-month trial with high (100 m⁻²/week) and very high (1,000 m⁻²/week) release rates. Experimental units without release of parasitoids served as control treatment. Gerbera plants were infested initially with 50–100 juvenile and 50–70 adult whiteflies in the first experiment, and in the second experiment with less than 50 juveniles per plant and 50–70 adults. Whitefly and parasitoid population density were assessed in weekly intervals using infestation and activity categories. Results show that parasitized whiteflies were present in all treatments within 2 weeks after initial release. Unfortunately, it was not possible to control whiteflies with standard release rates of E. formosa. Although parasitism rates slightly increased, the effect on whitefly populations was negligible. Large amounts of honeydew and growth of sooty mold fungi caused the termination of the first experiment. In a second experiment, E. formosa was tested at 10–100 times higher release densities. In contrast to the first experiment, whitefly densities increased steadily during the first 8 weeks, but remained constant until the end of the experiment in both treatments. Parasitism by E. formosa reached its maximum after 8 weeks. We discuss possible reasons for the low efficiency of E. formosa as a whitefly antagonist in greenhouse production of gerbera.     

Gas-filled root porosity in response to temporary low oxygen supply in different growth stages

The development of gas-filled root porosity in response to temporary low oxygen supply was tested for a range of edible and ornamental crops: rice, maize, wheat, sugar beet, tomato, cucumber, sweet pepper, carnation, gerbera and rose. In a first experiment, the roots of tomato, maize and gerbera had a higher gas-filled root porosity, E_p (% v/v), when grown permanently in a non-aerated instead of aerated solution. The E_p of roots increased during two weeks when half the root system of a young plant was transferred to a non-aerated solution; in older plants this response was not seen. Carnation had a negligible gas-filled porosity in all treatments. In a second experiment, a comparison was made between high (20 kPa) and low (about 2 kPa) O₂ partial pressure in a recirculating nutrient solution. Half of the root system was transferred to low O₂ at various growth stages. In most species older plants did not increase E_p on exposure to low O₂. For tomato, sweet pepper and rose, E_p was normally in the range 3–8% (v/v). Young plants of cucumber, wheat and sugar beet also had an E_p in that range, but in older plants values ranged from 1 to 3%. Transverse root sections examined by light microscopy showed, on average, 60% more intercellular spaces in the root cortex than the measurements of gas-filled porosity, probably because some gaps and spaces in the cortex were not gas-filled. This effect was most pronounced in tomato. A negative pressure in the cortex may be needed for gaps to be gas-filled. An exodermis may increase the effectiveness of gas spaces in the cortex by closing the gas channels and, by offering some resistance to water uptake, allowing a negative pressure head in the cortex which keeps gaps gas-filled. A redox dye method was developed to study the length of root which is effectively supplied with oxygen, as a function of E_p. Results indicated that for every percent E_p the root can remain aerated over at least 1 cm in a non-aerated medium under the conditions of the test.     

含矮壮素的保鲜剂对非洲菊切花衰老的影响

含矮壮素的保鲜剂能增加非洲菊切花瓶插衰老过程中SOD、CAT、POD的活性,削弱MDA含量的增加和的O-2生成速率,减少蛋白质的降解,降低脯氨酸含量和水分散失,维持膜结构的相对稳定性,延长切花瓶插寿命4 d左右.