The Kok effect in Vicia faba cannot be explained solely by changes in chloroplastic CO2 concentration.

The Kok effect - an abrupt decline in quantum yield (QY) of net CO2 assimilation at low photosynthetic photon flux density (PPFD) - is widely used to estimate respiration in the light (R), which assumes the effect is caused by light suppression of R. A recent report suggested much of the Kok effect can be explained by declining chloroplastic CO2 concentration (cc ) at low PPFD. Several predictions arise from the hypothesis that the Kok effect is caused by declining cc , and we tested these predictions in Vicia faba. We measured CO2 exchange at low PPFD, in 2% and 21% oxygen, in developing and mature leaves, which differed greatly in R in darkness. Our results contradicted each of the predictions based on the cc effect: QY exceeded the theoretical maximum value for photosynthetic CO2 uptake; QY was larger in 21% than 2% oxygen; and the change in QY at the Kok effect breakpoint was unaffected by oxygen. Our results strongly suggest the Kok effect arises largely from a progressive decline in R with PPFD that includes both oxygen-sensitive and -insensitive components. We suggest an improved Kok method that accounts for high cc at low PPFD.

A double-ratio method to measure fast, slow and reverse sap flows.

Sap velocity measurements are useful in fields ranging from plant water relations to hydrology at a variety of scales. Techniques based on pulses of heat are among the most common methods to measure sap velocity, but most lack ability to measure velocities across a wide range, including very high, very low and negative velocities (reverse flow). We propose a new method, the double-ratio method (DRM), which is robust across an unprecedented range of sap velocities and provides real-time estimates of the thermal diffusivity of wood. The DRM employs one temperature sensor upstream (proximal) and two sensors downstream (distal) to the source of heat. This facilitates several theoretical, heat-based approaches to quantifying sap velocity. We tested the DRM using whole-tree lysimetry in Eucalyptus cypellocarpa L.A.S. Johnson and found strong agreement across a wide range of velocities.

Primary breast lymphoma: the role of mastectomy and the importance of lymph node status.

OBJECTIVE: To construct and analyze a database comprised of all reported cases of primary breast lymphoma (PBL) that include treatment and follow-up information published during the last 3 decades. SUMMARY BACKGROUND DATA: PBL accounts for 0.4% of breast malignancies and 2% of extranodal lymphomas. Surgical therapy has varied from biopsy to radical mastectomy. Chemotherapy and radiation therapy have been used as adjuvant or primary therapy. A standard consensus treatment of PBL is not available. METHODS: We reviewed all published PBL reports from June 1972 to March 2005. A database was compiled by abstracting individual patient information, limiting our study to those reports that contained specific treatment and outcome data. Patient demographics such as survival, recurrence, and time to follow-up were recorded, in addition to surgical, radiation, and/or chemotherapy treatment(s). RESULTS: We found 465 acceptable patients reported in 92 publications. Age range was 17 to 95 years (mean, 54 years). Mean tumor size was 3.5 cm. Diffuse large cell (B) lymphoma was the most common histologic diagnosis (53%). Disease-free survival was 44.5% overall. Follow-up ranged from one to 288 months (mean, 48 months). Treatment by mastectomy offered no survival benefit or protection from recurrence. Treatment that included radiation therapy in stage I patients (node negative) showed benefit in both survival and recurrence rates. Treatment that included chemotherapy in stage II patients (node positive) showed benefit in both survival and recurrence rates. Histologic tumor grade predicted survival. CONCLUSIONS: Mastectomy offers no benefit in the treatment of PBL. Nodal status predicts outcome and guides optimal use of radiation and chemotherapy.