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H.P.V. Rupasinghe, K.C. Almquist, G. Paliyath, and D.P. Murr

We tested the hypothesis that conversion of 3-hydroxy-3-methylglutaryl co-enzyme A (HMG CoA) to mevalonate (MVA) catalyzed by HMG CoA reductase (HMGR) is the rate limiting step for α-farnesene biosynthesis of apples. In higher plants, isopentenyl pyrophosphate (IPP) is derived via two pathways: 1) the classical mevalonate pathway, and 2) the novel glyceraldehyde-3-phosphate (GAP)/pyruvate pathway independent of HMGR action. When apple skin discs were incubated with MVA, or GAP and pyruvate, MVA increased α-farnesene levels in the skin but not GAP and pyruvate. Treating apple fruits with Lovastatin (1000 ppm), a competitive inhibitor of HMGR, inhibited α-farnesene accumulation in the skin by 20% to 50% during storage. Content of α-farnesene in the skin increased during the first 2 to 4 months in storage, and then decreased. In contrast, HMGR activity, as determined by the conversion of [4-3H]HMG CoA to MVA in the total membrane and soluble fraction, was the highest at the time of harvest and gradually decreased during 5 months of storage in air at 0 °C. The potent ethylene action inhibitor 1-MCP inhibited ethylene production and α-farnesene evolution by 99% and 97%, respectively. The effect of 1-MCP on in vitro activity of HMGR was marginal (≈30% inhibition). 1-MCP inhibited respiratory CO2 evolution by 50%, which suggests also that inhibition by 1-MCP of α-farnesene synthesis in apple could be regulated by the acetyl CoA pool. In plants, HMGR is encoded by a small gene family and differentially expressed. As the first step of studying the molecular mechanism of HMGR regulation, we have isolated a 444-bp fragment of apple hmgr gene using apple skin mRNA and degenerate oligonucleotides designed against conserved regions of plant hmgr genes.

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Jean-Claude Pech

We have generated transgenic Cantaloupe Charentais melons expressing an ACC oxidase antisense gene in which ethylene production was reduced to less than 1% as compared to control untransformed fruits. As a consequence, some aspects of the ripening process were strongly inhibited (aroma volatiles production, chlorophyll and cell wall degradation, pigmentation of the rind, activation of peduncular abscission zone) while others remained unchanged (coloration of the flesh), allowing us to distinguish between ethylene-dependent and ethylene-independent pathways. Some postharvest characteristics of the transgenic fruit are described in terms of expression of ripening-related genes, respiratory behavior, and biochemical composition. Data also are presented showing that exogenous ethylene treatments could reverse the antisense phenotype.

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Graeme A. King and Stephen C. Morris

Compositional changes during the postharvest senescence of broccoli branchlets held at 20C in the dark were investigated, particularly during the first 24 hours. Major losses of sugars, organic acids, and proteins from floral, middle, and base sections of branchlets were detected during the first 6 hours. Between 12 and 96 hours, free amino acid pools increased (especially the amides glutamine and asparagine) for all sections of branchlets, while ammonia accumulated only in floral sections. Results are discussed in relation to the nature of the processes that set the tissues on the pathways leading to postharvest senescence.

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R.J. Griesbach

A regulatory gene, An2, controls structural genes within the flavonoid biosynthetic pathway. The inheritance of An2 expression in crosses between P. axillaris (an2) and P. exserta (An2+ ) was studied. Floral pigmentation was quantitatively inherited and involved the expression of a single regulatory gene (An2) and three structural genes (Hf1, An6 and Fl). White flowers were produced in an2- genotypes; while pigmented flowers were produced in An2+ genotypes. The intensity of pigmentation was determined by the interaction of An2 with An6, Hf1 and Fl, as well as substrate competition between the An6 and Fl encoded enzymes.

Open access

Jack W. Buxton and L. P. Stoltz

Abstract

The pentose phosphate shunt (PPS) was shown to be active in roses (Rosa hybrida L.). The C6/C1 ratio indicated that possibly as much as 50% of the glucose oxidized in the rose flower is through the PPS. However, the activity of the PPS in relation to the Embden-Meyerhof-Parnas pathyway-tricarboxylic acid cycle (EMP-TCA) pathway did not change significantly throughout the cut life of the rose. There was a drop in the respiratory rate of petals throughout the cut flower life. The inner petals exhibited a consistantly higher respiratory rate than did outer petals regardless of whether the flower was kept in water or preservative.

Open access

H. D. Rabinowitch and J. Rudich

Abstract

Green tomato fruits were treated with 2-(4-chlorophenylthio) triethylamino hydrochloride (CPTA) and/or (2-choroethyl)phosphonic acid (ethephon) and were stored for 10 days at a temperature of 32°C. CPTA-treated fruits developed red color mostly in the exocarp, while ethephon and no n-treated fruits showed yellow coloring. The combined effect of CPTA and ethephon on red color development was stronger than that of CPTA alone. As lycopene normally does not develop at high temperature it seems likely mat CPTA acts in a pathway different from the normal.

Open access

Daniel C. W. Brown

Abstract

More than 1000 higher plant species have been reported to regenerate in vitro via either somatic embryo formation or shoot formation (1, 9, 11, 12, 16, 27, 40, 42, 45, 46). Although many reports of plant regeneration are not accompanied by the necessary developmental or histological evidence for verification, it is apparent that most successes follow an organogenic rather than an embryogenic route. However, regardless of which developmental pathway is followed or the complexity of the protocol that is used ultimately to recover a complete plant, much of the work on in vitro regeneration can be described as empirical in nature.

Open access

R. W. Buescher

Abstract

The effects of ethephon concentration, maturity, and length of storage before treatment on red color development were determined in harvested rin tomatoes. Red color development was greater in fruits treated with 1% ethephon than in fruits treated with higher or lower concentrations. Ethephon-induced color was greater in fruits treated 42 days from anthesis than in fruits treated at 35, 49, 56, and 63 days. Less red color developed as time in storage before treatment increased. It is suggested that ethephon (ethylene) directs red color formation in rin fruits if it is applied prior to the onset of predetermined pathways which result in the expression of the yellow color.

Free access

Craig S. Charron, Daniel J. Cantliffe, Raymond M. Wheeler, Ara Manukian, and Robert R. Heath

A system and methodology were developed for the nondestructive qualitative and quantitative analysis of volatile emissions from hydroponically grown `Waldmann's Green' leaf lettuce (Lactuca sativa L.). Photosynthetic photon flux (PPF), photoperiod, and temperature were automatically controlled and monitored in a growth chamber modified for the collection of plant volatiles. The lipoxygenase pathway products (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate were emitted by lettuce plants after the transition from the light period to the dark period. The volatile collection system developed in this study enabled measurements of volatiles emitted by intact plants, from planting to harvest, under controlled environmental conditions.

Open access

J. V. Krans, J. B. Beard, and J. F. Wilkinson

Abstract

Leaf anatomy and CO2 compensation concentration (Γ) were used to determine the carbon fixation pathway for 10 cool season and 5 warm season turfgrass species. Turfgrasses of the subfamily Festucoideae were representative of C3 plants. Turfgrass species of the subfamily Panicoideae and Eragrostoidea were representative of C4 plants. Turfgrasses classified traditionally as cool season or warm season species correlated with C3 and C4 plant types, respectively. Both techniques of C3 and C4 classification proved equally reliable in this study, however, the utilization of Kranz leaf anatomy required less preparation.