George Yelenosky

Glycerol stimulation of chlorophyll synthesis, embryogenesis, and carboxylation and sucrose metabolism enzymes in nucellar callus of Hamlin' sweet orange

Phosphoenolpyruvate carboxylase (PEPCase) and sucrose phosphate synthase (SPS) were active in nucellar calli of ‘Hamlin’ sweet orange,Citrus sinensis (L.) Osbeck, grown on media containing either 5% sucrose or 2% glycerol as the primary carbon source. Activities of the enzymes, however, were much higher in the glycerol-grown tissues than those grown in sucrose. Glycerol, in addition, stimulated embryogenesis and chlorophyll biosynthesis and initiated the onset of ribulose bisphosphate carboxylase-oxygenase (Rubisco) activity. These stimulatory effects, which were not observed in sucrose-grown calli, became more obvious when calli grown on glycerol-containing, agar-solidified medium were transferred and grown in liquid suspension medium containing 2% glycerol. Starch levels in both sucrose- and glycerol-grown tissues were as high as 30% of tissue dry weight. There were, however, higher concentrations of soluble sugars in sucrose-grown calli than those grown on glycerol. Stimulation of embryogenesis, chlorophyll synthesis, Rubisco onset, and activities of PEPCase and SPS by glycerol offered potential prospects in using this compound in citrus tissue cultures.

Changes in glutathione content during cold acclimation in Cornus sericea and Citrus sinensis

Abstract Glutathione content was evaluated in relation to freezing tolerance in red osier dogwood stems and Valencia orange leaves. Exposure of dogwood and citrus to cold-acclimating conditions in controlled environments led to increases in reduced glutathione (GSH) content which were correlated with freezing tolerance. GSH did not accumulate in field-grown dogwood stems during cold acclimation in fall, but did increase in content prior to deacclimation in late winter. Further studies showed that accumulation of GSH in dogwood at low temperatures is dependent on adequate levels of sulfate in the soil. In citrus, modulation of GSH content by infiltration of leaf tissue with various compounds including GSH did not alter freezing tolerance. Root treatment with N,N -diallyl-2,2-dichloroacetamide (R-25788) increased leaf GSH content, but not hardiness. Evidence presented indicates that glutathione accumulates in plant tissues exposed to low temperatures, but that GSH accumulation is not associated with freezing tolerance.

Influence of growth regulator treatments on dry matter production, fruit abscission, and14C-assimilate partitioning in citrus

Experiments were performed to monitor (1) uptake and translocation of foliar-applied microdroplets of14C hormones and (2) effects of multiple growth regulator sprays on foliar and fruit growth variables and photosynthate partitioning in Valencia orange trees (Citrus sinensis (L.) Osbeck). The uptake of14C-sucrose,14C-paclobutrazol (PP333), and14C-napthaleneacetic acid (NAA) in 6-month-old greenhouse-grown trees exceeded that of14C-abscisic acid (ABA) and14C-benzyladenine (BA) 48 h after microdroplet application.14C-sucrose transport from the application site was much greater than any other source, especially14C-BA. In a second study, 2-year-old Valencia orange trees were maintained under field conditions and were sprayed to foliar runoff (3 × /week for 3 weeks) with BA, NAA, ABA, PP333, and gibberellic acid (GA3) at 100 μM during flowering and early fruit set. Select branches were then briefly exposed to14CO2 and harvested 24 h later. Both GA3 and BA sprays promoted foliar growth. BA also stimulated fruit growth, whereas GA3 sharply increased fruit dry weight while fruit number decreased. BA and GA3 enhanced14C assimilate export by the foliage to the developing fruit, and GA3 was especially active in promoting fruit sink intensity (14C/dry wt). The other compounds (NAA, ABA, PP333) restricted foliar and fruit growth. They also inhibited transport of14C assimilate from the leaves to the fruit. Results indicate that foliar-applied growth regulators can influence source-sink relations in citrus early in reproductive development by manipulating photoassimilate production and partitioning.

Changes in freezing tolerance and polypeptide content of spinach and citrus at 5 °C☆☆☆

Abstract The freezing tolerance of spinach leaf, petiole, hypocotyl, and root tissues and citrus leaf tissue was determined before and after 1 week of cold acclimation at 5 °C. Spinach leaf, petiole, and hypocotyl tissues increased in freezing tolerance upon exposure to 5 °C, while root tissue failed to show significant increased freezing tolerance. Citrus leaf tissue also increased in freezing tolerance following exposure to 5 °C. The protein composition of nonacclimated and cold-acclimated spinach leaf, hypocotyl, and root tissues and citrus leaf tissue was studied using two-dimensional gel electrophoresis and silver staining. Spinach leaf tissue exposed to 5 °C contained two cold-acclimation polypeptides (CAPs) (Mr 160,000 and 85,000) not found in nonacclimated leaf tissue. Numerous other changes in the polypeptide composition of spinach leaf tissue were observed following cold acclimation, but the appearance of CAPs 160 and 85 were the most consistent in all experiments. Cold-acclimated citrus leaf tissue also contained a polypeptide (Mr 160,000) not found in nonacclimated citrus leaf tissue. The similarity in molecular weight and isoelectric point between the CAP 160 of citrus and spinach suggests that these widely unrelated species may synthesize the same protein in response to exposure to low temperature. In contrast, both nonacclimated and cold-acclimated spinach hypocotyl tissue contained CAPs 85 and 160. However, cold-acclimated hypocotyls appeared to have concentrations of CAPs 85 and 160 higher than those of nonaccclimated hypocotyls. Protein analysis of nonacclimated and cold-acclimated spinach root tissue revealed no major qualitative differences. Furthermore, roots exposed to 5 °C did not synthesize proteins analogous to any of the CAPs synthesized in leaf tissue at low temperature. The inability of root tissue to synthesize CAPs at low temperature may be a factor in the lack of root freezing tolerance.

Influence of paclobutrazol in the soil on growth, nutrient elements in the leaves, and flood/freeze tolerance of citrus rootstock seedlings

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3ol] was applied to soil at 0, 100, or 250 mg/3.78-liter pot containing seedlings of Swingle citrumelo, Carrizo citrange, Cleopatra mandarin, sour orange, rough lemon, and Sun Chu Sha. All cultivars were sensitive to paclobutrazol, which caused a proliferation of shorter/thicker roots, and top growth showed shorter internodes and lower dry weight. Induced changes resulted in greater root/shoot ratios, and paclobutrazol treatments showed higher concentrations of nitrogen, calcium, boron, iron, and manganese in the leaves of different cultivars. Paclobutrazol-treated seedlings did not show a greater ability to tolerate flooded soil for 60 continuous days under greenhouse conditions nor survive-6.7°C controlled freeze tests. Paclobutrazol is a potentially useful plant growth regulator to dwarf citrus, but it apparently is not a strong candidate for increasing flooding and freezing tolerance in citrus rootstock seedlings.

Photosnythetic responses of rough lemon and sour orange to soil flooding, chilling, and short-term temperature fluctuations during growth

Abstract Soil flooding and cold temperature reduced leaf CO 2 exchange rate ( CER ) and activity of ribulose bisphosphate carboxylase-oxygenase (Rubisco) of rough lemon (RL), Citrus jambhiri Lush., and sour orange (SO), C. aurantium L. At growth-chamber conditions of low temperature (LT, 10°C) or high temperature (HT, 30°C), inhibitions in CER were 61% for flooded SO and 43% for flooded RL. For non-flooded trees, CER at LT was only about 27% that at HT. These inhibitions in CER were at least partially due to lower stomatal conductance. Reductions in Rubisco activity under prolonged soil flooding were about 30% at HT and 16% at LT. As a result of soil flooding, starch was higher in leaves, but was drastically reduced in fibrous roots of flooded trees under both LT and HT regimes. For non-flooded trees maintained at HT, starch was higher in leaves, but lower in fibrous roots as compared with non-flooded trees grown at LT. For trees maintained under the LT regime, activity of phosphoenolpyruvate carboxylase and concentration of proline in leaves were three- and 15-fold higher, respectively, as compared with trees grown at HT. Data on responses of CER to short-term fluctuations of temperature indicate that RL was more sensitive to sharp temperature variations than SO. Under prolonged soil flooding, however, RL was more tolerant than SO.

Effects of cold hardening on acyl lipids of citrus tissue

Abstract Cold hardened and unhardened 8- or 16-month-old citrus plants were examined for differences in fatty acid (FA) content. Unhardened leaves from 8-month-old Valencia scion budded on sour orange rootstock had 29% less FAs than leaves from seedling sour orange. After cold hardening triacylglycerol (TAG) FAs increased 4-fold in Valencia on sour orange and 6-fold in sour orange seedling. The percentage of FAs associated with TAGs for unhardened-hardened 16-month-old Valencia on sour orange tissues were: upper leaves 7–20, lower leaves 6–17, bark 6–9, and roots 57–73%. Cold hardening increased the amount of TAG FAs of 16-month-old Valencia on sour orange in upper leaves by 226% and in lower leaves by 173%. Concentrations of linoleic acid increased by 479% in upper leaves and by 303% in lower leaves. Quantities of lionolenic acid in monogalactosyl diacylglycerols declined by 27% in upper leaves and by 20% in lower leaves.

Subcooling in wood of citrus seedlings

Summary Differences in subcooling were apparent among unhardened seedlings of citrus varieties, but differences were not a satisfactory index of varietal differences in cold hardiness ratings.

Photosynthetic characteristics in leaves of ‘Valencia’ orange (Citrus sinensis (L.) Osbeck) grown under high and low temperature regimes

Abstract The photosynthetic activities of leaves of 1-year-old ‘Valencia’ orange (Citrus sinensis (L.) Osbeck) were determined after trees were maintained for 30 consecutive days in controlled growth chambers under high temperature (HT, 32.2°C day/21.1°C night) and low temperature (LT, 15.6°C day/4.4°C night). Leaf CO2 exchange rates (CER), stomatal conductance (Cs), transpiration (E), chlorophyll (Chl), soluble protein, and proline of the LT treatment were 48, 55, 26, 78, 113 and 265%, respectively, of the HT treatment. The water potentials (ψ) of leaves from HT treatment were about 0.5 MPa more negative than those from LT leaves. Activities of ribulose-1,5-bisphosphate carboxylase (RuBPCase) and phosphoenolpyruvate carboxylase (PEPCase) of the HT treatment, expressed on a leaf fresh weight basis, were 91 and 49%, respectively, of the LT treatment. PEPCase of both temperature treatments, however, showed no differences in affinities for HCO3− and PEP, having a Km (HCO3−) of 0.61 mM and a Km (PEP) of 0.15 mM. The ratio of RuBPCase/PEPCase was 6.6 for the HT treatment, compared to 3.5 for the LT treatment. When the 30-day HT-treated trees were transferred to the LT chamber, CER, Cs and ψ, determined 24 hr after transfer, were comparable to values of 30-day LT-treated trees; the RuBPCase activity decreased about 18% and PEPCase activity increased about 31% after 96 hr in the LT chamber. These relative changes decreased the RuBPCase/PEPCase ratio from 6.6 to 3.7. Switching trees from the 30-day LT treatment to the HT chamber resulted in increases in CER, Cs and E and decreases in ψ; the RuBPCase activity decreased about 10%, but PEPCase activity was relatively unaffected after 96 hr following the transfer to the HT chamber. The LT-induced changes in the ratio of carboxylase activities would indicate that some alteration in the photosynthetic carbon metabolism might occur in ‘Valencia’ orange leaf tissues subjected to cold acclimation conditions.

Non-structural carbohydrate concentrations in leaves of “Valencia” orange subjected to water deficits

Abstract Photosynthetic principal end products (starch, sucrose, and reducing sugars) were determined in leaves of “Valencia” orange (Citrus sinensis (L.) Osbeck) after trees were subjected to a 10-day, water-deficit period. Water deficit reduced concentrations of starch and sucrose, but not reducing sugars, in orange leaves. Starch content was reduced to 40–70% and sucrose content was reduced 30–75%. Reducing sugars in leaves of trees subjected to water deficit were higher than those of well-watered control trees, having increases ranging from 30 to 115%. Decreases in leaf starch and sucrose contents in “Valencia” orange due to water deficit apparently were the result of inhibitions in leaf photosynthetic CO2 assimilation, due in part to a reduction in stomatal conductance and presumably to a reduction in ribulose bisphosphate carboxylase activation and concentration.