Development and function of membrane systems in plant tissue. Annual progress report, 15 July 1974--14 July 1975. [Ion transport in corn roots]

Abstract

I. Research accamplishments Rese_Arch an mitochondrial ion transport has been stopped pending the return of Professor Hanson. Research on the development of enhanced ion transport in corn root tissue due to "washing" has continued. A. Mr. Willy Lin has continued the study of enhanced cell potentials developed with washing by investigating whether there are corresponding changes in cell resistance. (The terms "cell potential" and "cell resistance" are used since there parameters are measured between the vacuole. and the external medium, and thus refer to measurements across both .the vacuolar and cell membranes.) Washing proves to be without effect on resistance, which falls in the range of 11-13 megaohms in both fresh and 4 hour washed root tissue. There is thus no evidence to support the hypothesis that the increase in electrical potential is due to increased permeability, (Pk). Rather, the increased PD probably arises from energy-linked electrogenic transport, as previously deduced from the collapse of the increased PD with the uncoupler, FCCP (Plant Physiol. 54: 799, 1974). .-If enhanced electrogenic transport is responsible for the increase in PD with washing, the next question becomes, "what ion is being transported?". Mitchell's chemiosmotic hypothesis proposes that protan efflux pumping is responsible for salt transport; that is, an electrochemical gradient of protons-established by respiratory "loops" or K[P hydrolysis provides the potential for ion transport. Energy-linked proton efflux could then account for the electrogenic. transport component of PD. t However, we observed that net protan efflux was high in fresh tissue * reduced.

Exciton percolation in mixed molecular crystals and aggregates: from naphthalene to photosynthesis

“…We also notice that the present experimental information5,18 gives the region of ratios 0.1 < [B]/[A] < 1.0 (9) Actually there may exist much lower ratios than 0.1, but there is a difficulty in measuring such low ratios. 18 We note that the above considerations apply mainly to the "higher" (green) plants, containing large numbers of chromophores, with a nonzero B/A ratio as discussed, for instance, in ref 18, i.e., where both chl-a and chl-b are represented.…”