Cucumber cotyledons

Extracts from 152 plant species, representing 46 different families, were screened for effects on tobacco mosaic virus (TMV) replication in cucumber cotyledons. Twenty species have shown enough activity to warrant further study. Several members of the Caprifoliaceae family increased virus replication. An extract of Lonicera involucrata enlarged the virus lesions in local lesion hosts and produced a thirty fold increase in virus titer, but had no effect on virus replication in systemic hosts. The active material appears to affect the virus defense mechanism of local lesion hosts. An extract of common geranium is an active virus inhibitor. It inactivates TMV and TMV-RNA (ribonucleic acid) in vitro by forming non-infectious complexes. In vivo, it also inhibited starch lesion formation in cucumber cotyledons incited by TMV infection. 

Cucumber cotyledons were inoculated with purified tobacco mosaic virus (TMV) 20 to 24 hours before vacuum infiltration with different concentrations of crude water extracts of plant leaves (4). After 7 days, inoculated leaves were harvested and stored 24 hours in the dark in a moist chamber to remove excess starch. Starch lesions were counted after clearing with alcohol and staining with an iodine-potassium iodide-lactic acid mixture. The inhibitory effects of various extracts were demonstrated by comparing lesion counts of treated cotyledons to counts on control cotyledons. 

Figure 1. Effect of twinberry leaf extract infiltrated 24 hours after virus inoculation on TMV starch lesion development on cucumber cotyledons...

The treated cucumber cotyledons showing enlarged ringlike lesions were macerated in the presence of neutral phosphate, and the crude juice was inoculated into healthy cucumber cotyledons. Only dotlike small lesions were produced from such infections, indicating... 

Aqueous geranium extract inhibited TMV starch lesion formation in cucumber cotyledons. Starch lesions were completely inhibited by vacuum infiltrating effective dosages at any time between 1 and 33 hours after virus inoculation. Between 33 and 72 hours, inhibition decreased progressively. The active ingredient in the geranium extract was identified by means of ultraviolet absorption spectrum and... 

Figure 3. Virus titers of infected cucumber cotyledons infiltrated with different concentrations of tannic acid at various times after inoculation...

It was also linear over these same time periods, although at a reduced rate, for discs taken from 6-day-old cucumber cotyledons treated for 2 hr with 50 4 pphm ozone. 

Figure 1. Chlorophyll content and fresh weight of the cucumber cotyledon pair. O == untreated plants, X = 4 hrs at 24 2 pphm ozone and held 24 hrs before assay. Vertical bars indicate standard direction of the mean.

Effect of (-)-usnic acid (- -) and (+)-usnic acid (-o-) on electrolyte leakage from cucumber cotyledons. The arrow represents the time when the samples were exposed to 325 pmol m"2 s"1 light. Dashed line represents maximum leakage obtained from boiled samples and leakage from untreated samples are shown (- -). 

Kenyon W. H., Duke, S. O., and Vaughn, K. C., 1985. Sequence of effects of acifluorfen on physiological and ultrastructural parameters in cucumber cotyledon discs. Pestic. Biochem. Physiol. 24, 240-250. 

Cellular leakage as determined by changes in conductivity of treatments minus control conductivity changes of cucumber cotyledons as affected by exposure to different DHZ concentrations. Error bars are + 1 SE of the mean of six plates 50 pM acifluorfen used as positive control. Tissues were incubated in solutions in darkness for 18 h and then exposed to light. (From Galindo, J. C. G. etal. 1999, Phytochemistry 52, 805-813. With permission.)... 

Table III. Effects of BR and BA on SOD Activity in Etiolated and Greened Cucumber Cotyledons...

Cotyledon Expansion. Cotyledon expansion is markedly stimulated by GA and by BR as well, but to a lesser extent the activity is about 1/100 that of GA4. On the other hand, IAA has practically no effect Dark-grown cucumber cotyledons have also been shown to expand when subjected to BR treatment (6). Since expansion of cotyledons and leaves of intact seedlings is a normal effect of gibberellin, in this case BR acts like gibberellin. 

Ito H, Tanaka A (1996) Determination of the Activity of Chlorophyll b to Chlorophyll a Conversion During Greening of Etiolated Cucumber Cotyledons by Using Pyro-chlorophyllide b. Plant Physiol Biochem 34 35... 

However, wheat protoplasts have no other demonstrable responses to cytokinin and, therefore, the lack of a cytokinin effect on calcium transport is not a decisive test. Zhao and Ross [69] used zeatin induced growth and chlorophyll formation in excised cucumber cotyledons as cytokinin responses to examine the effects of calcium chelators, ionophore and several anti-calmodulin drugs. None of these drugs affected the two cytokinin responses unless used at concentrations high enough to cause indirect damage. 

Additional evidence that SA is transported from infected leaves to uninfected leaves comes from the experiments of Shulaev et al. [93]. They took advantage of the fact that in tobacco, the terminal step in SA biosynthesis is the Oj-dependent hydroxylation of benzoic acid to salicylic acid, a reaction catalyzed by benzoic acid 2-hydroxylase [94]. TMV-inoculated lower leaves of tobacco were enclosed in an 02-rich environment. The newly synthesized SA in these leaves was thus 0-labeled. Any radiolabeled SA detected in the upper uninoculated leaves would therefore have been synthesized and exported from the TMV-inoculated leaf. Approximately 70% of the SA in the upper uninfected leaves was found to be 0-labeled, confirming that SA is systemically transported from the infected leaf [93]. Similarly, the synthesis and transport of SA has been studied in cucumber using radiolabeled benzoic acid (BA) [95]. After administering C-labeled BA to cucumber cotyledons infected with C. lagenarium, C-SA was detected in the upper uninoculated leaves prior to the development of SAR. This C-SA was presumably synthesized in the infected cotyledons and subsequently transported to the uninoculated portions of the plant. 

Use of the cucumber cotyledon bioassay is limited because of probable differences in herbicide penetration and translocation. If all DPE herbicides affect the same site(s), then discrepancies in activity could also be related to the differential ability of cucumber cotyledons to detoxify these compounds. Further structure-activity studies must utilize in vitro assays to measure intrinsic activity. 

Figure 1. Efflux of from cucumber cotyledons in the presence of 1 mM DPE herbicides ( J. At time zero, cotyledons were exposed to 600 /m s (PAR) light and herbicide. Closed circles are efflux from untreated cotyledons. Abbreviations AFM, acifluorfen-methyl AFE, acifluorfen-ethyl.

By measuring the rate of Rb efflux from excised and preloaded cucumber cotyledons, AFM injury was detected at concentrations as low as 10 nM ( ). Also, because AFM has an absolute requirement of light for expression of herbicidal activity, plant tissues can be pretreated in darkness without injury. Then, following light-activation, damage can be detected in relatively short time periods (10 to 15 min) (1 ). We believe these observations are indicative of its primary biochemical mechanism of action. 

The activation of DPE s by light appears to require neither chlorophyll nor photosynthetic electron transport ( ). AFM will induce herbicidal injury in green and etiolated cucumber cotyledons in the presence of DCMU [3-(3,4-dichlorophenyl)-l,... 

Electron micrographs from cucumber cotyledons reveal the presence of large numbers of lipid bodies (oleosomes). 

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