Summnary. Participation of phytochrome 'is evident in the nyctinastic responise of leaves of Albizzia julibrissin (silk-tree), Albizzia lophantha, Leucaena glauca, Poinciana gilliesi and Calliandra inequilatera; closure of excised pairs of pinnules upon darkening is rapid following red illumination and slow following far-red. Fondeville, Borthwick, and Hendricks (2) reported on a role of phytochrome in the nyctinastic response of the sensitive plant, Mimnosa pudica: closure of the pinnules upon darkening was rapid when the darkness 'followed a brief red illumination and slower if the darkness followed far-red, with appropriate reversibility. The major significance of this report led us to see wrhether such effects could be obhserved in plants other than the relatively anomalous Mimosa, our imniedFate objective being an experimental system more stable and quantitative than that orig.nally described. This objective has now been attained well enough to provide, among other things. a rapid and dependable elenentary laboratory exercise. Materials and MethodsAlbizzia julibrissin (silk-tree), A. loplianttha, Leucaena glauca, Pointciana gilliesi, and Calliandra inequilatera were propagated iin the \varm greenhouse from seeds and cuttings. These species all have
Five field experiments were conducted in 1998 and 1999 in Minnesota to examine the influence of time of day efficacy of glyphosate [N-(phosphonomethyl)glycine] and glufosinate [2-amino-4-(hydroxymethyl-phosphinyl)butanoic acid] applications on the control of annual weeds. Each experiment was designed to be a randomized complete block with four replications using plot sizes of 3 x 9 m. Glyphosate and glufosinate were applied at rates of 0.421 kg ae/ha and 0.292 kg ai/ha, respectively, with and without an additional adjuvant that consisted of 20% nonionic surfactant and 80% ammonium sulfate. All treatments were applied with water at 94 L/ha. Times of day for the application of herbicide were 06:00h, 09:00h, 12:00h, 15:00h, 18:00h, 21:00h, and 24:00h. Efficacy was evaluated 14 d after application by visual ratings. At 14 d, a circadian response to each herbicide was found, with greatest annual weed control observed with an application occurring between 09:00h and 18:00h and significantly less weed control observed with an application at 06:00h, 21:00h, or 24:00h. The addition of an adjuvant to both herbicides increased overall efficacy, but did not overcome the rhythmic time of day effect. Results of the multiple regression analysis showed that after environmental temperature, time of day was the second most important predictor of percent weed kill. Thus, circadian timing of herbicide application significantly influenced weed control with both glyphosate and glufosinate.
Greenhouse and growth chamber studies were conducted to determine the cause of previously observed differences in the effectiveness of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] when applied at various times of the day to velvetleaf(Abutilon theophrastiMedic). Leaves of velvetleaf moved rhythmically from a near horizontal day position to a near vertical night position with the tip of the blade pointed downward. Plants were sprayed with bentazon at various times of day. The amount of spray retained and the degree of control decreased as the leaves moved toward the vertical downward night position. This suggested that a major cause of the time-of-day effect with bentazon treatments on velvetleaf is variation in the amount of spray intercepted and retained as a function of varying leaf angles.
Typha latifolia L. seed germination required high temperatures, low O2 concentration, and relatively long exposure to light to induce high percentages of seed germination. A greater percentage of seeds germinated at 35 °C than at lower temperatures. Less than 10% of the seeds germinated at 15 °C and none at 10 °C. For submerged seeds exposed to red light (R), maximum germination was achieved when the O2 concentration in the water was reduced to between 2.3 and 4.3 mg L−1 at 30 °C. Seeds were most sensitive to R when imbibed for 6–24 h. At least 10 h of continuous R (2.5 × 10−8 W m−2) was needed for maximum germination. However, when seeds were exposed to light of the same intensity for four 30-min periods over a 12-h span, the effect was nearly the same as 12 h of continuous light. The germination percentage after the intermittent irradiation was nine times that produced by a single 2-h exposure. Five minutes of far-red light (FR) reversed the effect of 6 h of R to the level of dark controls. The photoreversible effect of FR was less pronounced for seeds imbibed prior to illumination. When spans of R and FR were alternated (FR–R–FR, R–FR–R, FR–R–FR–R, R–FR–R–FR), repeated reversibility was observed. However, FR was progressively less effective in reversing the effect of R.
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