Probably inspired by increasing concern about our future energy supply, this unanswered question is attracting renewed interest (Terashima Selleckchem PF477736 et al. 2009; Björn et al. 2009; Raven 2009). It is often

pointed out that a mature leaf, especially that of a shade plant, does effectively intercept nearly all visible light. Some suggest that photosynthesis is not optimized for light absorption because other limiting factors prevail during most of the day. Another proposal is that chlorophyll was selected because of its redox properties rather than its absorption spectrum. It has even been proposed that chlorophyll-based photosynthesis see more evolved on account of shading by green-absorbing bacteriorhodopsin-based photosynthetic organisms (Goldsworthy 1987). To our knowledge, no one has challenged the assumption that black, or gray, would be better, with the exception of Lars Olof Björn in 1976 (Björn1976). The present study extends his analysis to optically thick systems and takes their energy cost into account. Theory By analogy to minimal models used to describe the competition for light in aquatic photosynthesis, terrestrial

photosynthesis may be modeled as a suspension of cells under constant illumination from above, but with two key differences: both light absorption by liquid water and the vertical mixing rate of the suspension become negligible. Only the species whose photosynthetic apparatus provides the most growth power at the top of the suspension will remain on top. As its population grows, it pushes its average down into its own shade until the lowest cells receive insufficient power

for their maintenance. This will be partially compensated for by adjustment of Ponatinib in vitro the amount of photosynthetic apparatus per cell, but its genetic modification to optimize the average growth power of the population will not be selected for, because the species would lose dominance at the top and be replaced. Solar irradiance provides an input of power in the antenna pigment systems that is the product of the excitation rate in light, J L, and the free energy, μ: $$ P_\rm in=J_\rm L \cdot \mu = J_\rm L \cdot kT \cdot \ln \left( \fracJ_\rm LJ_\rm D\right) $$where kT is the thermal energy and J D the thermal excitation rate at ambient temperature (Ross and Calvin 1967). Photosynthesis stores this absorbed power in chemical form with an efficiency P out/P in. The proteins involved in light-harvesting and CO2 assimilation constitute a substantial part of photosynthetic cells and their Selleckchem CDK inhibitor production costs must be correspondingly high.

The phase II COIN-B trial randomized patients to receive cetuximab and chemotherapy (Arm D) in an intermittent schedule versus intermittent chemotherapy with continuous cetuximab administration (Arm E). Upon RECIST progression on either arm, the same chemotherapy plus cetuximab was restarted and continued until progression. Continuous cetuximab administration as maintenance was associated with a longer CFI and longer this website PFS (5,1 and 13,7 months respectively vs 3,7 and 12 months in the arm D) [43]. The MACRO TTD phase III trial randomized 480

previously untreated mCRC patients to receive 6 cycles of bevacizumab and Xelox followed by Xelox and bevacizumab (arm A) or bevacizumab alone (Arm B). There were not statistically significant differences in PFS and OS between the 2 arms [44]. This study confirmed the efficacy of a maintenance therapy with bevacizumab after a predefined period of chemotherapy induction but did not investigated the role of bevacizumab maintenance in a stop-and-go strategy with a subsequent reintroduction of the same chemotherapy when disease progression HMPL-504 mw occurs. In the ongoing AIO study, maintenance treatment with capecitabine or 5-FU/folinic acid and bevacizumab is

compared with bevacizumab alone or no maintenance treatment in subjects with inoperable and non-progressive metastatic colorectal cancer after first line induction treatment for 24 weeks with a fluoropyrimidine-, oxaliplatin- and bevacizumab-based

chemotherapy. Reinduction treatment will be done in case of progression (Table 3). Table 3 Clinical evidences evaluating different strategies for treatment of mCRC EGFR therapy rechallenge – A multicenter phase II prospective study confirmed the activity of cetuximab rechallenge plus irinotecan-based therapy after an intervening chemotherapy [30] – A phase II prospective study did not show any response to panitumumab administrated after progression on prior cetuximab-based therapy [31] Chemotherapy stop-and go strategy – OPTIMOX 1 study shows that ceasing oxaliplatin after 6 cycles, followed by leucovorin–5-FU alone, achieves RR, PFS, and OS equivalent to that with continuing oxaliplatin Ribociclib ic50 until progression or toxicity [38] – OPTIMOX 2 study shows that continuing treatment with a maintenance chemotherapy led to a longer PFS, compared with pausing treatment [39] – COIN study did not show a non inferiority of chemotherapy free interval versus continuous treatment but treatment holiday significantly reduced cumulative toxic effects, and improved MM-102 mouse quality of life [41] Biological treatment of chemotherapy-free interval – NORDIC VIII phase III trial showed that cetuximab maintenance do not improve survival data comparing to intermittent treatment [42]. – COIN B phase II trial showed that cetuximab maintenance significantly improved chemotherapy free interval and PFS [43].