Root-Shoot Interactions in Peach: The Function of the Root

Peach seedlings were grown in aerated nutrient solution in small(15 cm³) or large (500 cm³) containers. Subsequently, some plantswere removed from the small containers to the large, or werestressed by root pruning. Half the plants received a foliarspray of synthetic cytokinin 6-benzylaminopurine (BAP) every4 days. Analysis of all the results enabled correlations between functionand growth measurements to be made. Irrespective of the treatmentthe total water and the total nutrient uptake by the roots wasdirectly related to the total dry weight increment. This suggeststhat for both water and nutrient uptake a functional equilibriumexisted between the root and the shoot. Where BAP treatmentincreased the top: root ratio there was a corresponding increasein the rate of water uptake per unit length of root. The relationship between root number and leaf number and thecomplementary action of BAP suggests that the root tip and itsproduction of cytokinins exerts considerable control over topgrowth.     

Balance between Potassium and Phosphorus in the Nutrition of Barley: I. The Influence on Amine Content

Potassium-deficient barley accumulates the amines agmatine andputrescine, the latter of which is known to produce necroticspots on the leaves in some seasons. The severity of potassiumdeficiency symptoms is strongly influenced by the external levelof phosphorus. An experiment was conducted in water culture,using two-week-old barley to discover whether amine accumulationwas similarly affected. Four levels of potassium —1/64,1/6, 1/4, and 1/1 of full supply—were combined factoriallywith the same levels of phosphorus, the diagonal in this designbeing a series of ‘balanced’ solutions in whichpotassium and phosphorus were present in the same ratio as inthe full nutrient. The plants were sampled three times duringthe ten-week period of growth, and the form of the results wassimilar each time. Whenever potassium was reduced, putrescinecontent rose above normal, but for large amounts of putrescineto be accumulated, phosphorus supply had to be in excess ofpotassium. The highest levels of agmatine were also found wherepotassium was low and phosphorus in excess, but significantaccumulations also developed whenever phosphorus was low relativeto potassium, that is, where high levels of potassium were observedin the plants. Since agmatine and putrescine are very closely related biochemicallyand together make up 90 per cent of the amine content of barley,the influence of potassium and phosphorus on their summed contentwas considered. Potassium was found to have the dominant effect:at any one level of phosphorus supply, the summed content wasminimal at the highest level of potassium, and reduction inpotassium always increased it. The effect of phosphorus dependedon the degree of imbalance between potassium and phosphorusin the nutrient. High summed contents were found where eitherpotassium or phosphorus was present in excess, and minimum contentwas found where the levels were balanced. There were significantpartial correlations between summed amine content and the potassiumand phosphorus contents of the plants. The high significanceof correlations between amine content and the proportion ofdead and moribund shoot material suggested that amine accumulationmight be partly responsible for the rapid death of the leavesof the deficient plants as well as for the production of necroses,which are only limited in area.