Phase Change in Hedera helix L: I. GIBBERELLIN-LIKE SUBSTANCES IN THE TWO GROWTH PHASES

Gibberellin-like substances were extracted from all parts ofthe juvenile and adult growth phases of Hedera helix. A numberof extraction techniques were employed and estimatos of theamount of gibberellin-like activity present were made usingthree bioassays. Gibberellin like substances were present inapproximately equal amounts in leaves at the two growth phasesand appeared to be localized, in the main, in chloroplasts.Apical ‘buds’ of the juvenile phase were shown tocontain higher levels of gibberellin-like substances than theiradult counterparts. Roots, which under normal circumstancesare associated only with the juvenile phase, contained highlevels of extractable gibberellin-like substances.     

Phase Change in Hedera helix L.: III. THE EFFECTS OF GIBBERELLINS, ABSCISIC ACID AND GROWTH RETARDANTS ON JUVENILE AND ADULT IVY

Gibberellic acid, applied to delaminated petioles of rootedcuttings of juvenile and adult ivy initially induced internodeelongation and abnormal leaf development, and suppressed apicaldominance. Juvenile cuttings were affected only transientlyand soon reverted to normal growth. Adult cuttings, insteadof resuming normal growth after this initial response to GA₃,gradually developed many juvenile characteristics. Approximately16 weeks after treatment at 25 ?C nearly all shoots of adultcuttings had undergone complete rejuvenation. Lower temperaturereduced the speed of response to GA₃. A mixture of gibberellinsA₄ and A₇ had effects similar to those of GA₃ on the growthof juvenile and adult cuttings. Treatment of both phases ofivy with abscisic acid (ABA) induced no visible effects andwhen ABA was applied with GA₃ it did not reduce the responseof either phase to the gibberellin. CCC had a marked dwarfingeffect on juvenile ivy but did not induce pre-maturation. However,extraction of gibberellin-like substances from severely dwarfedplants suggested that CCC was not exerting its growth retardingeffect through an inhibition of gibberellin biosynthesis. AMO1618 did not retard growth of juvenile ivy cuttings.     

Phase Change in Hedera helix: Induction of the Mature to Juvenile Phase Change by Gibberellin A3

A sensitive and reproducible method to obtain GA₃ induced morphological reversion of mature Hedera helix to the juvenile form has been developed. Dose response experiments indicate that GA₃ stimulates reversion over a 50–100 fold range with a half maximal response at approximately 0.5 μg GA₃ per plant. The individual characteristics involved in phase change revert to the juvenile form in a sequential manner as GA₃ dose is increased. Variations in light intensity from 1.2–3.6 × 10⁴ lux and temperature from 15 to 26°C do not affect this hormonal response. Other growth regulators including indoleacetic acid, kinetin, abscisic acid and (2-chloroethyl)phosphonic acid (Ethephon) are inactive but other gibberellins (GA₁ and a mixture of A₄–A₇) are active in stimulating reversion. Therefore, the response is specific for gibberellins as a class of hormones but non-specific for a particular form of gibberellin. The significance of this response in relation to juvenility in woody plants is discussed.     

Phase Change in Hedera helix: Stabilization of the Mature Form with Abscisic Acid and Growth Retardants

Applications of ABA to the mature form of Hedera helix stabilize its morphological characteristics and prevent GA₃ induced reversion to the juvenile form. Plants treated with GA₃ reverted to the juvenile form whereas those supplied with ABA in conjunction with GA₃ remained mature. When mature plants were treated with 5 nanomoles of GA₃ and 5 micromoles of ABA, reversion did not occur, but when the GA₃ dose was raised to 25 nanomoles with the same level of ABA, reversion did occur. This implies that the relative amounts of GA₃ and ABA applied are important in controlling growth form and not the absolute levels of these hormones. Applications of growth retardants (Chlormequat, Ancymidol, and SADH) stabilize the mature form by preventing spontaneous reversions induced under low light intensity. These two lines of evidence support the hypothesis that the mature morphological form can be stabilized by regulating the effective level of gibberellins in the plant and this can be accomplished by inhibition of gibberellin action or gibberellin biosynthesis.     

THE PICEA ABIES SHOOT APICAL MERISTEM IN CULTURE. II. DEPOSITION OF POLYSACCHARIDES AND LIGNIN-LIKE SUBSTANCES BENEATH CULTURES

Excised shoot apical meristems of Picea abies seedlings grow and develop primordial leaves when cultured on Millipore (mixed esters of cellulose) filter membranes lying on a simple, defined medium gelled with agarose. When the cultures are removed from the membranes, each leaves a spot of altered light transmission, spectral characteristics, hygroscopicity, and chemical reactivity. These spots are the manifestation of deposition in the membrane pore space of polysaccharides, lignin-like components, and probably other substances. Deposition of water-insoluble, Schiff's reagent-positive substances can be detected in the filter membranes after only 3–6 hr exposure to a meristem and continues for 10–15 days or longer. Precursors of the insoluble deposition materials can diffuse through at least nine layers of Millipore membrane before deposition at a site remote from living cells. Placement of a dialysis membrane between the meristem and the Millipore membrane prevents detectable deposition in the latter. The observations are consistent with the hypothesis that apical meristems can synthesize and export mobile precursors of cell wall components as well as any substances necessary to promote their condensation or polymerization into insoluble materials at remote sites. The system may be useful in studying synthesis of cell wall components and investigating the functional role of growth regulators in shoot apical development.     

Studies in Dormancy of Sycamore: II. THE EFFECT OF DAYLENGTH ON THE NATURAL GROWTH-INHIBITOR CONTENT OF THE SHOOT

1. An investigation was made into effect of daylength conditionsof the inhibition content of first-year seedlings of sycamore(Acer pseudoplatanus). 2. The shoot apical regions and mature leaves were extractedwith 80 per cent. Aqueous methanol, fractionated by paper chromatographyin isopropanol/ammonia and assayed by the wheat-coleptile growthtest. 3. A growth inhibitor was present in all extracts at R_f 0.7.Higher levels of inhibitor were present in both apices and matureleaves of plants transferred to short-day conditions than ofthose maintained under long-days throughout. 4. These difference in inhibitor level can be detected after2–5 days of short-day treatment, Preceding any markedeffect of daylength on growth. 5. Evidence is adduced in support of the hypothesis that theinhibitors is produced in the leaves during darkness and istransported to the apex during the photoperiod.     

Studies on Isolated Protoplasts and Vacuoles: II. THE ACTION OF GROWTH SUBSTANCES

The response of isolated protoplasts to indol-3-yl acetic acidwas investigated, and they were found to undergo a rapid water-uptakewith ultimate rupture of the plasmalemma and release of thelarge central vacuole. The use of a photomicrographic methodshowed that this response was optimal at 10^-5 M indol-3-yl aceticacid. No such response could be detected for isolated vacuoles.¹⁴C-labelled indol-3-yl acetic acid was used to obtain furtherinsight into the site of action of this growth substance. Evidenceis presented which suggests that the site of action of indol-3-ylacetic acid, for this response, is the plasmalemma, where itfacilitates an increased uptake of solutes which is followedby an osmotic water uptake.     

Growth and Development in the Young Tomato: II. THE EFFECT OF DEFOLIATION ON THE DEVELOPMENT OF THE SHOOT APEX

In tomato seedlings the effects of high temperature in delayingthe enlargement of the shoot apex and of increasing the numberof leaves produced before flowering, were counteracted by removalof the first two leaves during the early vegetative phase. Inplants grown at 25° C. defoliation was followed by rapidenlargement of the apex and earlier flower initiation, the numberof leaves produced before flowering being reduced to that inplants grown at 15° C. Defoliation of plants grown at 15°C. resulted in only a slight increase in the rate of apicalenlargement, and the time to flowering and number of leaveswere unaffected. Growth analysis showed that at the time ofremoval, the first two leaves were not self-supporting and at25° C. were utilizing a much higher proportion of assimilatetranslocated from the cotyledons than at 15° C. These resultsare considered to support the view that at higher temperatures,the first two leaves compete strongly with the shoot apex forsupplies of assimilate.     

THE THEORY OF DIFFUSION IN CELL MODELS : II. SOLUTION OF THE STEADY STATE FOR THREE DIFFUSING SUBSTANCES

The differential equations describing diffusion in cell models have been extended to include the simultaneous penetration of water and two salts. These equations have been solved for the steady state. Values for the concentrations in the steady state which may be computed from the equations compare favorably with the experimental values obtained by Osterhout, Kamerling, and Stanley. Moreover, it has been shown elsewhere that the solution for the steady state is essential to a discussion of the volume change or "growth" of phase C in the models and, by analogy, in living cells.     

COMPARATIVE STUDIES ON RESPIRATION : II. THE EFFECT OF ANESTHETICS AND OTHER SUBSTANCES ON THE RESPIRATION OF ASPERGILLUS NIGER.

1. In concentrations which are high enough to produce any effect, formaldehyde, ether, and acetone cause an increase, followed by a decrease, in the rate of respiration. 2. 3.65 per cent ether, which causes an increase with certain cultures, produces only a decrease with others. 3. The reaction producing an increase in the respiration with 7.3 per cent ether is a reversible process, while the reaction producing the decrease is not reversible. 4. 0.5 per cent caffeine produces only a decrease in respiration while a saturated solution causes an increase, which is followed by a decrease.