Alfalfa saponins as inhibitors of cotton seed germination

The inhibitory effect of alfalfa saponins on the germinationof cotton seeds was primarily attributed to interference withthe seedcoat and with the membrane. This effect was not dueto impermeability to water. ¹This work was supported in part by grant No. FG-Is-246 fromthe U.S. Department of Agriculture, and a grant from the Committeefor the Encouragement of Research, General Federation of Labour,in Israel (Received December 8, 1969; )     

Effects of Moonlight on Flower Induction in Pharbitis nil, Using a Single Dark Period

Flowering of Pharbitis nil plants was slightly inhibited byexposure to the light of the full moon for 8 or more hours witha single dark period of 16, 14 or 13 h. It is suggested thatin the natural environment moonlight may have at most only aslight delaying effect on the time of flower induction in short-dayplants. Flowering, moonlight, night-break, Pharbitis nil, photoperiodism, short day plants     

Gibberellins and Inhibitors in Relation to Flowering of White Clovers (Trifolium repens L.)

Flower primordia appeared sooner and flowering intensity increasedas day length was extended beyond 8 h (short day) in two whiteclovers: cv. Tamar and cv. Tammisto, originating from Israeland Finland, respectively. Application of GA₃ under short dayscaused Tamar to flower more intensively as much as the doseof GA₃ was increased, but it did not affect the flowering ofTammisto. The level of gibberellin-like substances in stolon apices washigher under long (16 h) than under short days in both cultivars.The level of inhibitors extracted from leaves was not affectedby day length in Tamar. However, in Tammisto this level wasalmost twice as high under short than under long days. It issuggested that the presence of a relatively high level of inhibitorsin Tammisto when grown under short days interfered with theactivity of gibberellins in its effect on flowering. ABA wasamong the inhibitors: its application under long days had noeffect on flowering, but it increased the number of stolons.Possibly inhibitors other than ABA are involved in the preventionof flowering. Leaf expansion responded to day length and GA₃ and ABA applicationin a similar way as the response of flowering, i.e. towardsflowering the size of the leaves increased.     

Hormonal Regulation of Morphogenesis and Cold-resistance: II. EFFECT OF COLD-ACCLIMATION AND OF EXOGENOUS ABSCISIC ACID ON GIBBERELLIC ACID AND ABSCISIC ACID ACTIVITIES IN ALFALFA (Medicago sativa L. SEEDLINGS

The endogenous levels of gibberellin and abscisic acid weredetermined in extracts from seedlings of alfalfa (Medicago sativaL.) ov. Hairy Peruvian and cv. Ranger, growing under long daysand high temperatures (not inducing cold-hardiness), or shortdays and low temperatures (inducing cold-hardiness). Under inductiveconditions only Ranger was coldacclimated, exhibiting a rosettegrowth; non-acclimated seedlings of Ranger and Hairy Peruviandeveloped an elongated shoot. Under non-inductive conditionsgibberellin A₃ (GA₃)-like activity was found in both cultivars.Under inductive conditions GA3-like activity increased in HairyPeruvian and was almost non-existent in Ranger. In spite ofmorphological modification, ABA-like activity was hardly affectedby thermophotoperiod conditions. Addition of ABA to the nutrientsolution of seedlings growing under non-inductive conditionssimulated the effects of short days and of low temperatures.It diminished GA3 content, and affected morphological modificationof the seedlings. It is concluded that the modification of theABA/GA balance, through the decrease of the GA level, monitorsthe capacity of the twoalfalfa cultivars to become cold-acclimatedwhen exposed to low temperatures.     

Lucerne Saponins as Inhibitors of Cotton Seed Germination: THEIR EFFECT ON DIFFUSION OF OXYGEN THROUGH THE SEED COATS

The site of inhibition of cotton-seed germination by lucernesaponins seems to be associated with tissues other than theembryo. The rate of water uptake during imbibition was similarfor intact seeds immersed in water and for those in 0.5 percent saponin solution. Seeds previously immersed in saponinsolution showed a lower rate of respiration, absorbing about60 per cent less oxygen than those pre-immersed in water. Yetthe respiration rate of excised embryos from both treatmentswas the same. The extent of the inhibition of germination wasnot affected when oxygen was either bubbled through the saponin-containingimmersion-solution or passed through the flasks in which theseeds were germinated after 24 h of pre-immersion. The rates of oxygen diffusion through the seed coats and membranesof seeds pre-immersed in water or in saponin solution were measured.They were distinctly lower for seed coats and membranes whichhad been exposed to the saponin treatment. It has been concludedthat the seed coat and/or the membrane of intact cotton seedspre-immersed in saponin solution serve as a barrier for oxygendiffusion to the embryo, resulting in inhibition of germination.     

Hormonal Regulation of Morphogenesis and Cold-resistance: I. MODIFICATIONS BY ABSCISIC ACID AND BY GIBBERELLIC ACID IN ALFALFA (MEDICAGO SATIVA L.) SEEDLINGS.

Seedlings of alfalfa (Medicago saliva L.) cv. Ranger and cv.Hairy Peruvian were grown under conditions of long day and hightemperatures or short day and low temperatures. Under long daysand high temperatures, both varieties developed an elongatedshoot and exhibited relatively low cold-resistance, as measuredby the extent of leakage of cellular substances, after beingexposed to sub-zero temperature. Under short days and low temperatures,Ranger seedlings developed a rosette growth and exhibited animproved response to sub-zero temperature. In contrast, HairyPeruvian seedlings developed an elongated shoot and did notacquire cold-resistance. Hairy Peruvian grown in a nutrientsolution containing abscisic acid, however, developed a rosetteand acquired an improved response to sub-zero temperature, likecv. Ranger under short days and low temperatures. Addition ofgibberellic acid to Ranger seedlings grown under these conditionsnullified the environmental effects, since they developed anelongated shoot and did not acquire cold-resistance. It is concludedthat abscisic acid and gibberellic acid are involved in theinterrelationship between morphogenesis and cold-resistancein the seedlings of the two alfalfa cultivars.