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David J. Ballantyne

The influence of photosynthetic photon flux density (PPFD) and gibberellic acid (GA3) sprays on shoot elongation was determined for `Coral Bells' (Kurume or R. obstusum hybrid), `Fashion' (Glen Dale or R. indicum × Kurume hybrid), `Hexe' (R. obtusum × R. simsii hybrid), `Hinocrimson' (Kurume or R. obtusum hybrid), `Hinodegiri' (Kurume or R. obtusum hybrid), and `Red Wing' (Brooks hybrid) azalea. GA3 at 1 mm was more effective in stimulating shoot elongation of `Coral Bells', `Fashion', `Hinodegiri', and `Red Wing' than of `Hexe' or `Hinocrimson'. GA3 sprays were more effective in stimulating elongation when applied to plants growing at irradiance levels of 350 μmol·s-1·m-2 than to plants growing at either 200 or 100 μmol·s-1·-2. Gross photosynthesis of leaf segments was higher for a slow-growing cultivar (Hinocrimson) than for a faster-growing cultivar (Fashion). `Hinocrimson' produced stouter shoots (greater dry weight/cm) than did `Fashion'.

Open access

Connie S. Bozarth, Robert A. Kennedy, and Kurt A. Schekel

Abstract

For all leaf ages of Rosa hybrida L. cv. Samantha, maximum photosynthetic rates were reached at irradiances of 450 to 500 μE m−2sec−1. The magnitude of this response decreased from 20.6 mg CO2 dm−2hr−1 in the youngest leaves studied to 15.4 mg CO2 dm−2hr−1 in the oldest. Maximum photosynthetic rates were reached before full leaf expansion. Mesophyll resistance, however, increased with age from 7.8 to 12.5 cm sec−1. CO2 compensation points and dark respiration decreased throughout most of leaf development, but increased slightly at the most advanced developmental ages studied. Photosynthetic enhancement, the percent increase in net photosynthesis at 2% O2 compared to 21% O2, averaged 33% for all leaves. There was no change in the amount of photosynthetic enhancement as leaves aged, indicating that changes in photorespiration were not a major factor in photosynthetic trends over the range of leaf ages examined.

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Daniel Leskovar and Yahia A. Othman

measured 15 weeks after the N application in each year. Gas exchange measurements were conducted between 1100 and 1300 hr from two fully expanded leaves. Gas exchange measurements were determined using a portable photosynthesis system (LI-6400XT; LI

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Jean-Pierre Privé, Lindsay Russell, and Anita LeBlanc

net photosynthesis (Pn) were achieved at a higher frequency of kaolin particle film application and that this was particularly the case at leaf temperatures exceeding 35 °C ( Privé et al., 2007 ). Ultraviolet damage and photoinhibition can be additive

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D.E. Deyton, C.E. Sams, and C.D. Pless

Four-year-old `Gala' and `Widjit' apple trees with significant apple aphid populations were sprayed to runoff on 13 May 1994 with 0%, 0.5%, 1.0%, or 2.0% (v/v) emulsified degummed soybean oil (SO) or with 1.0% petroleum (dormant) oil (PO). Treatments were arranged in a randomized complete-block design with five single-tree replications. Apple aphid populations were determined on 10 tagged shoots per tree. The top fully expanded leaf of two randomly selected shoots per tree were tagged and net photosynthesis (Pn) and transpiration (Tr) measured. Trees treated with SO or PO had <20% as many aphids after treatment as nontreated trees. Trees treated with 2% SO had lower Pn and Tr than the control for 18 days after treatment. Spraying 0.1% or 0.5% SO caused less initial reduction of Pn than 2.0% SO, and the effect was shorter lasting. Four-year-old `Oregon Spur' and `Empire' were sprayed with 0%, 0.1%, 0.5%, 1.0% SO or PO on 26 June. Treatments were arranged in a randomized complete-block design with four single-tree replications. Pn rates of trees treated with 0.1% to 1.0% soybean oil were <40% of nontreated trees the day after treatment, but recovered to >80% of control in 5 days.

Open access

T. B.G. DelValle, J. A. Barden, and R. E. Byers

Abstract

Greenhouse studies were conducted to identify a chemical that would temporarily suppress net photosynthesis (Pn) of peach leaves. Antitranspirants and photosynthetic inhibitors were tested on leaves of greenhouse-grown peach trees [Prunus persica (L.) Batsch]. Leaf dips of 8% Vapor Gard (poly-1-p-methen-8-9 diyl), 10−3 m ABA, 10−3 m diuron, and 10−3 m terbacil reduced Pn by more than 50% within 1 day after treatment, without causing excessive visual phytotoxicity. Since terbacil strongly reduced Pn with minimal phytotoxicity, it was applied as limb treatments to bearing ‘Madison’ peach trees in the field. Treatments were single applications at 1000 or 2000 ppm, double applications a week apart at 1000 ppm, or 2000 ppm at week 1 followed by 1000 ppm at week 2. Fruit drop was 73% to 90% on terbacil-treated limbs compared to 20% natural drop on nonthinned controls. All terbacil treatments increased the size of remaining fruit over that of the nonthinned checks. The 1000 ppm treatment resulted in fruit size similar to the hand-thinned check, but higher concentrations caused smaller fruit than the hand-thinned control.

Chemical names used: abscisic acid (ABA); N’-(3,4-dichlorophenyl)-N,N-dimethylurea (diuron); 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione (terbacil).

Open access

Bruce W. Wood

Abstract

Seasonal measurements of net photosynthesis (Pn), stomatal conductance (Cs), and endogenous senescence-related chemicals were made on pecan [Carya illinoensis (Wang.) C. Koch] trees growing in the orchard environment. Leaves from terminal shoots of mature, 75-year-old ‘Moneymaker’ trees in the “on” alternately bearing phase maintained 10% to 40% higher Pn rates than did those of “off” phase trees. These “on” leaves also maintained higher levels of chlorophyll, protein, amino acids, and RNA, but less K. than “off” leaves. The presence of developing fruit suppressed the rate of late summer and autumnal leaf senescence, with “on” trees retaining their leaves in a higher state of vigor than those of “off” trees. Pn and Cs rates between leaflets of adjacent fruiting and nonfruiting shoots of 7-year-old ‘Desirable’ trees were also 10% to 15% higher for the fruiting shoots throughout the season. Pn and Cs rates were influenced such that gas exchange of leaves increased as sink demand increased. These data provide evidence that this sink-demand associated stimulus operates in a localized rather than a generalized manner and that it retards the rate of leaf senescence.

Free access

Lingyun Yuan, Yujie Yuan, Shan Liu, Jie Wang, Shidong Zhu, Guohu Chen, Jinfeng Hou, and Chenggang Wang

and accelerated senescence. The photosynthesis in C 3 plant is more sensitive to HT, especially the photosynthetic apparatus ( Wahid and Rasul, 2005 ). HT differently affects the stability of many proteins and membrane system and alters the efficiency

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Chuhe Chen, J. Scott Cameron, and Stephen F. Klauer

179 ORAL SESSION (Abstr. 715-722) CROSS-COMMODITY PHOTOSYNTHESIS

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Benyamin Lakitan, David W. Wolfe, and Richard W. Zobel

Abbreviations: BBL, `Bush Blue Lake 274'; DAP, days after planting; g,, leaf conductance; LN, `Luna'; Pn, photosynthesis; ψ L , leaf water potential. 1 Current address: Fakultas Pertanian, Universitas Sriwijaya, Palembang 30139, Indonesia. 3 Dept